Adding Third Engine (lower HP) for docking / idle / etc.
 

Something I've thought about, that I would love to hear anybody's opinion / information on - would be adding a third engine - not a third engine of equal performance with a third stern-drive, but a third engine of much lower horsepower.

I had originally thought about using one of those those really small stern drives - but realized that using a third stern-drive would interfere with the two main drives.

We boat from our canal, and have almost 20 minutes from the time we start the engines to the time we can power up. Additionally, we cannot leave early or late due the noise and neighbor complaints. It would be real nice to be able to use something small (like 80-110 hp) to move the boat.

I had thought about mounting a jet-ski jet-drive (or something similar) low on the transom - something low profile that wouldn't drag while the boat is on plain, and wouldn't get in the way of the cross-member between the other two stern-drives. How well do you think this would work ? I know there'd be a lot to do with steering (two wheels, perhaps?) but is the idea at least worth considering ?

I was hoping to build it up enough to get the boat near plain or on plain (with the two stern-drives lifted), but the primary purpose would be to move the boat at idle speed without burning extra gas and pissing off neighbors.

I have a 30' Scarab (See my other posts), with twin 454's and TRS's.

Thanks,
Paul Rohrbaugh

Sounds Cool
 

The idea sounds great not sure how you are going to make it work with 2 wheels and another drive dragging in the water.

Make sure to post pictures if you do it.

Why I wanted to go with a jet drive - Figured there would be little or any drag. Just raise the two TRS's out of the water when you wanted to use it, and I might even be able to get it on plain. I figured I would mount a smaller size engine in front of the other two (Probabily a V-twin of some sort), and run a shaft under the oil pans of one of the 454's.
~Paulr

Very interesting topic. On the raising of whatever you install, use a lever arrangement that when the TRS goes all the way up the whatever goes down. Use a rising rate lever so that it does not go down until the TRS is almost all the way up. Perhaps the jet drive is the right track, doubt you would ever get anything above a fast no wake though. Pick up the water through the hull and pipe it to the jet?

Through the hull is what I've thought about, I've just been wondering about where. You need a pretty big hole to get water in, but I don't want to be forcing water into it from forward motion and causing extra drag. I had thought about bringing it in on the side below the water line. Just "Idle speed" is all I really need, haven't brought the Scarab home yet, but the neighbors complaned about the Chris-Craft with 350's with wet exaust (Under the fiberglass swim platform too!). Those 454's will make them REAL happy...

Interesting idea with the lever, not exactly sure how it would work. .prettymuch sure a third drive wouldn't work - you would need to raise the third drive to go fast - and lower the TRS's. The linkage between the two is right in the way... (unless you had the third drive so high the prop wouldn't be under the hull)

Another issue would be the strengh of the transom. Wouldn't putting a 4" to 6" hole in the bottom create some structureal issues (As well as a similar sized hole on one or both sides)? What, if anything, would I need to do to reinforce this ?

And yes, if I do this I will definetly post pictures.
Thanks,
Paul Rohrbaugh

What about mounting a small jet drive outboard on the transom so that it is not lower than the keel. It would be under water when off plane and when on plane would be above the water. You could probably tie it into the steering of the outdrives. Hmmm?

A jet drive would create a HIDEOUS amount of drag.

The pump intake will scoop water up and direct it thru the pump regardless of whether the jetdrive motor is running or not.

I can only assume you are talking about using an outboard of some sort (jet or otherwise), especially since the motors in the 30 Scarab are not mounted far enough apart to allow anything to be mounted between them.

An sailboat-style outboard kicker bracket will mount on your transom and allow you to drop it for your long slow ride to open water, and then it will swing the motor up and out of the water once you get there. There are some newer ones that some pro bassboat guys are using that will handle a 30hp foustroke outboard.

You aren't going to get your boat to plane with less than 100hp, so just go ahead and forget that part of it. And since you aren't going to get it to plane with a 30, you might as well stick with a lighter 9.9 or something.

Another option may be to use a couple of cavitation plate mounted trolling motors and carry a Honda EU200i generator to not only keep the batteries charged for the trollers, but to run a carryon A/C while you cruise slowly in the searing heat. Those boogers are MEGA QUIET.

hydraulic steering on the drives, so it'd have to be an external system (which could get messy with trimming the drives). Could probabily get it to work with some engineering. However, I don't have things like welders so any work will require some planning. There's also the issue of appearance, so I'd prefer to go with an internal system, even with the extra work involved, unless this proved completely impossible.

I don't have a specific engine in mind (could use some help with that too), but I was hoping to use some sort of a V-twin or perhaps a V4 (a straight engine would be too big, unless it was mounted sideways - which would be really hard). I figured I could get it in the 80-120 HP Range while keeping it relatively quiet (doesn't have to be silent - just no WWII bomber noise) - which would be hard to do with an outboard.

I guess going at 2MPH would be better than running those 454's at 6 in the morning, but I'd prefer to "open her up" and get up to a good 5 or 6 MPH :).

Already wrote all this when mcollinstn replied.
I planned on putting the intake on the side of the boat to prevent the drag, most of the sides are out of the water when on plain. I Planned on mounting a SMALL V-twin in front of the engines, it would just be hard to work on them (Seeing as the third would probabily weigh only 120 or so pounds, it could be pulled if necessary). If you think I would only really small horsepower, I could go with a single-banger Briggs or Honda, It'd still be better than an outboard hanging off the back.

I had thought about trolling motors - I've only seen them up to .5HP - would one HP of force even move the boat ? It's currently 8300 pounds, and I DO Want to get going a good 5/6 MPH.

I guess if I am stuck with an outboard sobeit, but I was really hoping for an internal setup.

Thanks for all the feedback,
Paulr

I saw a post a while back (OSO?) where a guy had a 36 Skater that he rigged twin Lycomings turbine engines and Arneson surface drives. As you could imagine, this was probably a handful docking anywhere/anytime. I think he (and the Coast Guard) was most concerned about the balls of flames that shot out the exhaust. :cool:

He set up a couple of bad a$$ trolling motors on the transom, and lowered and raised them with a couple of jack plates for outboads. He slaved the steering off the drives. Pretty slick.

I don't think that anything you can do will get it close to plaining off, so you should target something with just enough speed to putt around at no-wake speeds. Twins are always better for maneuverability.

Good luck,
Brian

Wouldn't it just be a lot easier to run a Silent Choice or Q&Q type exhaust? Or are they not available for TRS's?

My Cigarette has Gills with adjustable baffle plates. It's only twin small blocks but not too loud at idle with the plates closed. You could also run just one engine untill you get to open water. Just altnerate engines so you keep the hours even.

Briefly searched but didn't find anything, I'll search again in a bit. I guess I've never seen anything resembling a "performance" trolling motor. I found an equation online, and based on it, i would need 208 pounds of thrust. And I doubt that would be anywhere near 5 MPH. I'll keep my eyes out for 12V units, but after doing a quick google search, anything over 50 pounds thrust appears to be 24 or 36V (A beast I do not want to tackle)

Brian:

Even if it were, the boat has dry exaust and I want the performance that offers, and I would rather use an outboard then re-do the exaust. I also want it loud when I am running :).

Even then, the community I live in has a large quantity of elderly persons - It'd take a lot of work to get those 454's as quiet as what I have now, and that is just marginally accepted. That would also probabily cost more than an outboard, and as much as one of the other ideas proposed. I'd rather have a second system (low on fuel / low noise / etc) - and still have the ability to have it be heard when I'm out on the river, etc. On my chris I did go out on one engine, but I didn't think to alternate, so the hours are a bit out of sync.


For the short term or for the long term if necessary, I'll just take the boat out during hours when everyone's up - to keep everyone form getting really pissed. It's just nice to leave at 6 or 7 on a Saturday and beat some of the traffic.

Thanks,
PaulR

What about diverting the exhaust completely under water? If you do use a prop, maybe the folding low drag types used on sailboats would help. I think electric power may be a good way to go. Even extra batteries or a generator would weigh less than the equivelant engine. If you could get a big enough jet mounted and figure a way to power your steering maybe you could leave a drive down and use it as a rudder for steering.
Im no marine engineer, but I did stay at a Motel 6 last night :crazy:

No sort of non-marine engine can be placed in your engine compartment, ESPECIALLY AN AIR COOLED ONE !!! (pretend that there are about seven thousand exclamation points there).

Only something along the lines of a jetski motor or something can be placed inside the boat. And the smallest of those is around 30 hp (the short lived Kawasaki 250cc jetski motor is the smallest).

A side inlet on a jet drive would be more or less do-able, but you now have to run a length of reinforced fiberglass tubing around in your engine compartment. I just don't see it being a "good thing". Nor do I see it being particularly helpful.

Most trolling motor propellors are designed for appx 5mph. I'd say that twin 42 (or 54's if you need them)pound cav mounts would push your boat 5 mph easy, if you were running Alpha drives where the props would freewheel. Bravos and TRS drives will most likely drag the props (not turning) at 5mph (Bravos might spin the props, but I'd venture that TRS's won't). Might still get 5 mph out of her even with the props not spinning.

It would sure be easy enough to find out: borrow two trolling motors, make a temporary bracket off your swim platform, rig two batteries together, and hang the trolling motors securely just behind your outdrives.

If this works, it is your cleanest option. You may need the generator, though, for this to work, cause two of these running wide open for an hour will suck the life completely out of a pair of batteries.

As far as noise, the Honda generator is very very quiet, and you will just pull it out and sit it on the swim platform for your slow ride.

Also, though, you seem to be under the misconception that small outboards are not quiet. You obviously haven't been around some of the modern "silent" 4 strokers...

Appears to be a "rough" correllation in comparing thrust to horsepower in a lowspeed pusher application:

54 pounds of thrust is roughly equivalent to a 1hp motor.

Well I have seen Arnesons tunnel with those little electric motors. OK around the docks or to load / unload but you will not get very far very fast. Nice idea just do not think they would work well or you would be happy with that set up.

Probably the easiest is to quiet your existing exhaust. Some type of switchable that would get you under the water would work. Switchable so you can let it rumble in the open water. Saw the sorcerer tunnel a few years ago with some very exotic exhaust diverters. It was amazingly quiet when it was on. Man that thing rumbles when uncorked though!! :D

Just my .02. Good luck

If I Can find suitable 12V units, I may go that route. Still not sure exactly how I would mount them, part of the appeal of the origional jet drive idea would be that nothing would be visible with the boat in the water. A second steering Wheele wouldn't be impossible, but not preferred. With the batteries, I plan on installing two 8D batteries in addition to what it already has for Audio Equipment and an Inverter, so those could power a trolling motor as well.

mcollinstn:
I don't think the cooling would be a problem, but that is a point I really hadn't given much thought to until now. I am still mainly interested with the jet drive idea, with the trolling being a secondary. However, if it's mounded on the cav plate, what about the drag while I am under way ? I don't know anyone offhand with two spare trollers, but I can look around. Power probabily won't be an issue, as I will be installing those extra batteries.

Generator is a good idea, but if I am going to be doing this with some frequency I would prefer to mount the generator in the compartment. Again, the heat would probably be an issue.

I have never seen a quiet small outboard, I have seen quiet big ones however. Either way, I don't want to be sitting on the swim platform steering the boat, and I don't want the outboard hanging on the back end while on plain. Whatever I do, I want it to look slick, or as cool as possible. This isn't a 'rush' situation, so I can do the research to get exactly the system I need.

I've seen small trollers mounted on Trimtabs, but have no idea how many pounds they were, or how they affected the trimming. If those have enogh power and won't screw up the trimming, that may be a real option. Whatever I use, it has to be 12V.

At idle (4.6 MPH GPS or so), it takes me almost 15 minutes to reach the river, where I could turn on the main engines if I Wanted. I have another 3-5 minutes until I can actually power up, but this could be done under the main engines if necessary. If a trolling setup could get going 5 MPH for 15 minutes and then charge on the river, it might be an option (and a lot less painful then either the jet drive or the silent exaust - which I am not hot on). Either way, the outboard is my absolute last resort.

Thanks to everyone for all their feedback!
~Paulr

OK, so I was off a bit... 33 Daytona, single 1,800 HP Lycoming T-53-13B Turbine, and a 6-drive.. Here's some pics for an idea how he rigged it:

http://www.hotboat.net/classifieds/a...bine%20Daytona

Don't know about the thrust numbers on his, but he seemed to make it work. I saw an article somewhere else about it, so you might do some additional searching for "33 Daytona Lycoming" and see what comes up.

Brian

Wow brian, that's Quite a setup. It looks rather slick, too. Haven't found too much mention of it on the internet, but I am still searching. Found the main listing. That's a good idea with the hydraulic setup. I just sent him an Email inquiring how he set it up, and how fast it moves, thank you for this reference. Wow, 135 MPH. If anyone else has any more ideas, please post them.

Now that I know about all these other options, I probabily won't consider the jet drive unless I can get enough horsepower to get it up on plain.

Too bad turbines are so expensive....

Thanks to everyone,
~Paulr

You guys might want to check with Howard Arneson or Rik They have done everything you are talking about. Howard's turbine setups do not use a transmission Maybe you can find. something on his web site We did a twin turbine cougar cat with a 90hp jet drive Yamaha with a high lift jack plate but the jet ski setup is the cleanest deal

No! I could care less how well a lawnmower motor or a portable generator will cool in your engine compartment. That's not even a tiny concern at all.

The concern is that a non marine engine or device in your engine compartment WILL BLOW YOUR BOAT UP.

As in BOOOM.
Wouldn't give a rat's @ss whether the generator or mower motor was cool or not when it exploded your boat into a giant fireball.

Have you never heard of USCG approved devices? They are required in any engine compartment. You know, the engine compartment that gets filled with gasoline fumes from non-USCG generators and lawnmower motors that are bolted in there. That's the one I'm talking about...

And a quick question: you mention you are going to drop 8D's into it and an inverter. What exactly are you planning to do with the inverter? Power TV's and fans? or something more?

If you run a couple of 8D batteries, you can definitely run the trollers with no generator. You can also flip a quick switch and run them on 24v from the 8D's (or from whatever pair of batts you are using). If you plan to do this, though, you gotta use the correct type of battery switches. You don't gotta stick with 12v trollers.

As far as switchable exhaust, there's no reason why you can't adapt a captains call style setup to your boat, which will dump the entire exhaust out the prop hub underwater like a Bayliner. Just a bunch of bubbling sound. No rumble. Flip a switch and you got loud and nasty again. You seem to be avoiding that easy option and wanting to bore giant holes in your boat and mount explosive lawnmower grenades in your engine compartment. i am not sure I understand...

As far as the trim tabs, sure, I see no reason why you can't mount trollers on the tabs. That sounds like a good place for them.

And here's another idea.
How much thrust do you need to make your boat go 5mph? Get a ski rope and a meat scale (it'd be great if it reads up to 300 pounds, but 150 one will do for this purpose). Get a towboat and hook your Scarab to the towboat on the ski rope and put the meat scale on one end. Pull your boat at different speeds and read the towing power required to make it coast at different speeds. You can even drop the drives to see how much it matters. If you can get adequate speed with 100# of pulling force, then the trollers should work. If you need 300# to get the speed you want, then you know you need a 6hp setup.

as long as you have a flame arrestor over the carb on the third engine, and the exaust sealed all the way outside the boat, there would be a very marginal increase for the chances of an explosion, especially if you run the blowers like you're supposed to. The only other source of ignition would be from the magneto. If I were to use a generator, I would probabily buy one for marine applications.

8D batteries:
*one mono amp - will be running two JL 12W7 Subs, amp will be doing about 1500 Watts
* one 4 channel amp - will run two 12W3 Subs, as well as all components. Will be doing about 1000 Watts
* Interter - probabily a 1500 watt or 2000 watt inverter - for TV / computer / power tools / whatever.

That'd be a draw of around 210 Amps at 100% volume (asuming 100% efficiency), so I will definetly need the 8D's. I planned to put an isolator on each engine's alternator, and go straight to the second bank of the 8Ds (But that's a whole different story).

If I were to go to 24V, I would have to rig up something with relays to go from series to parallel. I guess it's an option - but I would rather keep it all 12V.

The reason I wanted to "Bore Giant holes" was to avoid the performance loss (minimal, granted) of switchable exaust, and the work involved with mounting it, as well as the thought I would be able to get the boat to plain. Once I realised that 120 or so HP wouldn't do it (now that I think about it, I realise I would need 300+ HP), I became interested in other options. If this type of exaust setup will not be terribly expensive and won't hurt my performance much in the open mode, I might be interested. However, I am not familiar with how they work - would I need to move my current exaust tips ? Would I need new risers / manifolds ? I don't see how it could fit any other way.

As of right now, I am about equally interested in a drop-down style setup like the 33' turbine boat has (for easier steering), and the trim-tab setup. If the silent exaust would be favorable enough, I might go that route instead.

That's a good idea you have with using the scale, I'll try to do it whenever I get a chance, but only to see if it's even possible with trollers - If I went that route I'd put on the biggest setup I could to combat any unforseens - wave action / wind / engine failure / etc.

If it came to it, I could probabily fit two trollers on each of those Kplanes, which would definetly do it (almost 350 LBs from what I've seen for 12V).

On a tangent: What I was previously thinking about instead of a generator was a 8-12 HP manual start engine with a 80-110 Amp marine alternator on it, to charge the 8D's from the Audio usage (and now the trolling usage, I guess). I've seen devices like this before, but never in marine applications. Since you don't like mower engines, what would you suggest ? My primary usage would be lots of DC amps, not AC - I guess I could run the chargers off a generator but my idea seemed simpler.

Thanks,
Paulr

how bout this ? If you have a swim Platform you could build a stainless bracket aound the platform ...mount the motor to the bracket and the idea is NOT to be on a plane and the jet is just under the surface ..when you go to sterndrive power the boat is lifted and the jet is out of the water and no drag .....

How about a couple of these? :D :D :D j/k

Switchable exhaust has been around for years. Quite surprised you aren't familiar with it. No real drawbacks Other than an additional 30 pounds for the exhaust yokes (assuming you don't currently have them on your boat) and maybe 5 more for the actuator pump.

You're still not hearing me on the USCG thing. (and I like lawnmower engines just fine on lawnmowers). If you wanted to use one in the boat, you would need to:
#1: have a separate fuel pump for it cause fuel will not gravity flow in a boat. The fuel pump would need to be either a small marine electric pump or a jetski style diaphragm pump.
#2: The carb(s) on the motor would need to have a closed venting loop put on it to keep sticking floats from drooling gas into your bilge.
#3: flame arrestor.
#4: if it had points (which they don't anymore) then you'd have to change it to cdi.
#5: you have to remove any of the factory "kill switches" that short to ground via open (non marine) switches and run a remote kill switch with the proper switch (out of the engine compartment).
#6: You'd have to fabricate your own water cooled and water jacketed exhaust system for it, because no exposed item can be over (is it 450 degrees?) a certain heat level in an enclosed compartment to avoid vapor combustion.
#7: You'd have to run for sure with the blower on at all times
#8: if it's a air cooled motor, you'd have to run with the hatch open, which makes it louder than most of the other choices mentioned (and definitely louder than underwater exhausts on your main engines).

Your expected use of the inverter is appropriate. Just checking since I've heard people talk about installing an inverter to power their battery charger before... (not suggesting you would make that suggestion, but just checking anyhow).

24 volt switching can be done.
Only one battery is permanently attached to ground.
In 24 volt mode, one battery still supplies 12 volts to whatever needs it, while the other is plumbed in series (with its "-" pole removed from the grounding system) to shoot 24 to the trollers. To be honest, both batteries can still provide 12 volts to other accessories at the same time, but they must be feeding two separate unconnected systems- so it is easier to just drop to one feeding 12v and the other used to provide 24.

Most portable generators (Honda included) have a DC outlet on them. It is normally, though, a smaller output (8 amps @ 12vdc in the case of the Honda). Two inexpensive chargers can be used far more effectively.

If you ran 2 trollers wide open (50 amps x2 @ 24v), you would suck your 8D's empty in a little over 2 hours.

You don't like the idea of an outboard on the back, although a Honda 9.9 weighs 115 pounds and a Honda 20 weighs 135 pounds. Can't say that I blame you, but they are by FAR the most sensible addition in the way of adding additional powerplants. (a 2hp weighs 30 pounds - and is the equivalent of FOUR trollers, and a 20 would be the equivalent of FORTY trollers if the rule of thumb I found is correct).

Do yourself a BIIIIIIGGG favor, and look into switchable exhaust.
http://www.rexmar.com/page234.html
http://www.marineparts.com/partspage...a-Gil/GIL6.htm
http://www.marineparts.com/partspage...omparisons.htm
http://www.corsaperf.com/mbrochure3.htm

quiet like a baby.

Simple is ALWAYS better on a boat. If the issue is noise, get a silent choice system.
If you NEED another motor, get a small O/B, mount it on a bracket above the keel so there's no drag when you're running on the IOs. Tie it into your existing steering.
BTW, You're going to need a lot of batteries to move an 8000lb boat for 20+ minutes on an electric trolling motor.
Gary

Are the stern mounted thrusters (like bow thrusters) much different from trolling motors? Would they be an option here if they were oriented fore and aft instead of sideways?

Been there, tried that ( as steering motors around the dock on a single engine boat) They worked great to steer but when ever you did a tite ( as in anything where the boat leaned 10 degrees or so) turn at speed it ripped the props blades off the hubs, even the "unbreakable" composite ones. They were mounted on top of the trim tabs so were protected on plane and were ok as long as I kept turns to the flat easy 1/4 mile radius variety but in tite turns there was enough side blast/spray to destroy them:( , I think I musta had a lot of (to much) time on my hands the summer I tried that :D

I know how it is when you get an idea for doing something a certain way, when an easier solution is obvious. You're just looking for a challenge aren't you?

For less than the cost and complexity of adding a silent drive, you could design or source a better silent choice system. Formula had the right idea with their silent thunder swim platforms with integral exhaust. Nobody in their right mind would complain about the noise from that system. You could build something similar to fit under your swim platform that could work even better. Do it right and you will have a product to sell.

The voice of experience!:D

P.S. I only used them as steering around the docks so just hooked them up to the house batteries avoiding the generator issue and this was fine cause they were only used for a couple minutes or so while docking. Control was via a couple DPDT toggle switches on the dash driving 3 relays which switched /reversed the power to the actual motors, required as the curretn involved is signifigant 30-50 amps depending on the motors.

Yeah, I could see that being a problem (props falling off during a turn). I'll look into that silent exaust - if I do a project it'd be easier to adapt one of those systems to work with my dry exaust then mess with any other systems.

Still am not keen on messing with the 24V, but I guess I could to it if absolutely necessary. re: the engine - thanks for the information on installing one. I would look (and hope to find) a smaller size one with water cooling already, but that is nowhere near first priority. First, I need to install the closed-cooling, then Sient Exaust or maybe the drop-down trollers

I WOULD prefer an alternate engine system, but I am not going to go with outboards. I'm at work right now, so I can't go to all of those sites or talk more.

Thanks for all the feedback,
Paul Rohrbaugh

Just to give you the other parameters. I used 55 lb thrust motors and with both running the boat would go a little faster than with the main engine at idle so probably 4-6 mph,,, but,,, in no wind and smooth water, in 15kt wind was probably all they could do to hold it in place. There is a comercial unit which mounts to the outdrive above the cavitation plate for trolling and as I said on the tabs just doesn't work, trim was not affected they just kept breaking props

Thanks.
Does anyone have any experience with the cav plate models ? Do they cause / have any problems of their own - I would think they could cause some extra drag at low to moderate speed as they'd be in the water stream. I know a picture of one was included in a previous post - but there was no information given as to how well they works.

I'll check into the silent exaust when I get home - I'll have to give this some thought as to which route I go - heck, I may do both in the long run - they both seem to have their usages.

Thanks to everyone for their input,
~Paulr