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21' Diesel Nordic in Feb. Powerboat mag

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Old 02-07-2008, 01:27 PM
  #21
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Originally Posted by baywatch View Post
I'll have to look when it warms up. I should have 55" not sure about a full 60."
I was thinking mabye B-max drives as an alternative to the ASD's? I have seen a few sonics with b-max's hooked to yanmars, but not sure how trouble free they were.

I will take better pics and measure once it warms up.
What about the Arneson/Bravo conversion kit? The rear of your engine would stay in the same spot.
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Old 02-08-2008, 12:51 AM
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baywatch & Payton,

The reason I ask is simple, baywatch is you are serious about converting to diesel in the future I made want to help you. If you read my notes (5 pages) on the other diesel thread here you see I make refernce to a gear box. I might be willing to dust that off and make you a set of those so you can run your same bravo drives.

This is not a tomorrow thing, I need to rework the design a little, build a proto and slap it on a genset for 1,500 hrs.

Now Konrads or Arnesons??? Depends on what you want to do.

I don't know what ratios Konrads come in but here is where RIK and myself disagree. I will give him credit that his turn a big wheel slower advise is good for 99% of the boats out there. It's the little 1% of the world that I have spent years playing in.

In my experience running the diesels in open water where you had to actually throttle a boat (not just cut the engines back) when we tried big wheels, the second you move that throttle back and props loose a little bite the diesels loose boost. With the big wheels you just can't accelerate the engines quick enough to get that back and boat just flops rather than fly like a gas boat.

The bigger reduction gear also works in reverse now because of the prop drag and further holds the engine back. Here's an example when you push start a car do you use first gear or high gear? You use high gear which is less reduction, the same with a prop, the water grabs it like push starting a car in 1st gear.

Again, if you are just crusing, high speed running on the smaller lakes, bays, etc. That big prop provides good top speed, great cruise speed and great economy - RIK is right.

Run the boat from Sandy Hook to AC with a 20 knot South and wind and you'll suck wind!!

Again, my opinion alone.
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Old 02-08-2008, 03:18 AM
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Propeller RPM is dependant upon application. Displacement and application determine rpm.

Slower is more efficient is an argument the cruisers all rave about, but at the same time a fat boat will not get on plane or stay on plane with a shallow ratio.

There are trade offs to each.
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Old 02-08-2008, 11:57 AM
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RIK,

If you were to do his 36 Apache and convert it to Arneson's and let's say I gave you 425 Hp (crank) at 3,000 rpm's - how would you set-up the boat? You have many more applications to draw from than me and you never know I just be a customer again sometime soon?

The boxes I talk about were a means to an end, can't sell engines if people needed to rework the whole boat and I assume your bravo conversions were designed for that same reason to sell more drives.

FYI - I will more than likely challenge what you post as a response to this simply because I want to debate this application and see where it goes. On a personal level I would love to see more people with diesels and maybe your drives (LOL), I think a good airing could help that?

Joe Gere
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Old 02-08-2008, 12:17 PM
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[QUOTE=HabanaJoe;2437536]In my experience running the diesels in open water where you had to actually throttle a boat (not just cut the engines back) when we tried big wheels, the second you move that throttle back and props loose a little bite the diesels loose boost. With the big wheels you just can't accelerate the engines quick enough to get that back and boat just flops rather than fly like a gas boat.QUOTE]

That is an excellent point, as soon as you get off the gas under load in a diesel, you loose boost and it falls flat on its face. Seems you have to slowly load the engine to get it into high boost under load. I noticed that in my friends Ford F250 Powerstroke pulling a boat over the pass. It was perfectly happy pulling over the pass at over 70 mph. As soon as someone pulled in front of us, he had to let off on the gas. The trans downshifted and it took a while to load it up again in high gear to get back to speed.

Do the new diesels have blow off valves like the newer gas turbos? The blow off valve would allow the turbo to stay spinning when the throttle is chopped for a breif time (this keeps the turbo spinning while shifting gears). As soon as the throttle is re-opened the blowoff valve closes and it is right back to boost.
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Old 02-08-2008, 04:22 PM
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Propster,

There are two type of valves that I think are similar to your description (these are their high level functions):

Pop-off valve - This in on the intake side, when boost pressure is too high it will allow the engine to relieve some pressure as to not make to much horsepower.

Waste-gate - Exhaust side, when using a small turbo you can actually have exhaust pressure that exceeds intake pressure, when that happens engine can't breath anymore and power goes flat. It lets the engine loose some of that pressure.

Neither of these devices helps keep the turbo spooled up as far as I know? With a waste gate as soon as you lift off the throttle the exhaust pressure and temp drop and the waste gate closes. In theory I guess with a small enough turbo you could keep enough flow to keep it spooled up?
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Old 02-08-2008, 06:21 PM
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Key things:

36' OAL

10K Displacement

Non Step Bottom

Goal top speed

Use a 1.13:1 reduction ratio. Use a Hering 18.25 X 31 5 blade propeller.

Should reach 66-67 ish.

His goal of twin 480's would reach 72-74
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Old 02-08-2008, 06:45 PM
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RIK,

You my friend are good, yes you are, you have a gift!

Name the the movie and I'll send you a shirt!

I think it will go a little faster, a little under proped, I think you could 72-75 from it, with 425's.

Why such big dia. and not OD?
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Old 02-08-2008, 07:05 PM
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Would have to know more details about its current performance in order to get an accurate synopsis.

Don't think 10K lb will want to stay on plane well with od and small diameter with only what, 33' bottom??. It would want to fall off real fast below 30 mph and not make a happy boater.

Would need a 7 blade propeller and we are starting to reach for special things in order to make things work on that path and then who can afford the special things?

Vicarious learning:

388 Slingshot has let's say a 34' lwl? Beam 8.5' and with a pair of 440's with a displacement of 9,000 lbs will reach 84-85ish.

Stepped bottom and for the most part an pretty efficient bottom.

Example #2

37' OL with twin 420's cat's with a displacement of 10,000 lbs and a beam of 8.5' will reach 74-75 max.

Once again a somewhat efficient bottom.

Now, take a non stepped, and somewhat not known as an efficient bottom, add weight and the results will be lesser.
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Old 02-08-2008, 07:33 PM
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Ok, but first what movie is the line from?????

7 blades - extreme!

I agree with the fall of plane theroy but why is he able with the Bravo drives to stay on plane? I'm guessing the props are small and with the hubs the blade area is not much and they are probably 4 blades?

baywatch - tell us about what the boat does now, how much HP, what size props, at what rpm can you stay on plane down to?
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