Question about outboards??
 

Has anybody converted an IO boat to outboards?? What are the rule of thumbs for horsepower on outboards vs Big Blocks?? Any pics of boats with outboards please post thanks!!

Not aware of a slide chart...
 

Not aware of a power slide chart for conversion of IO to OB, but it is a somewhat common occurence.

You are sort of asking a wide open general question.

I know I am missing something, but there are a number of things which need careful inspection, if not rebuilt. Transom, knees, stringers, corners, cap.

Seldom are OBs directly mounted to the transom, so a decision needs to be made which style of mounting you wish.

Mounting OBs also opens up a vast array of pocketing possibilities

I am sorry I really haven't addressed your principal question, but for the most part since this is a performance boat forum, I would think you might hang as big a motor(s) as you have room, boat size and bank account for!

On larger offshore boats (27++ deep vees) OBs will run pretty much same talking apples to apples.
Meaning a boat with twin 300hp I/O will run roughly about same with 300hp OB
I know on the Carrera 27s like mine the ones with twin 300hp small blocks ran same as twin 300 OBs
though not as well balanced in my opinion.
After that things get not so clear..
Problem is with OBs you are limited to about 300-350 an engine, only way to get more is to put
more engines, this creates drag in the water from the extra gearcase which robs some of that
new found power, thus a triple 300 OB may have 900hp but will be slower than a twin 450hp I/O.
Some guys even go with 4 or 5 outboards but again the more gear cases in the water the power it takes to push them. 4 300hp would put you at 1200hp but you would not be anywhere near as fast
as twin 600hp I/Os..
Some boats are excellent OB material, Cats for one love them especially the smaller lighter ones.
Most Center Consoldes are OB powered, forgetting about the fishing side of it most peaple get CCs
for partying, taking the motors outside the boat opens up a huge area.

Other things to consider is cost, typical 300-350hp OB runs 15-20k, about same as a 496/bravo setup,
Not bad if you stick with 2 of them but once you start running 3-4 pf them it adds up quick.

You are moving all the engine weight further back, this can adversely affect your ride in rough water.

If you also like rafting up and hanging out you will have no swim platform space , even with just 2 OBs
you will have to jump around them. Means everyone on your raftup will be walking on your boat
to get by instead of the platform.

Just random stuff I could think off..
If you have an Active Thunder 32 like your name says triple 300s will get you in the low to mid 70s,
youll cut back on gas use probably by 20-25% and the conversion will probably run you around $75k
using new motors+bracket+controls,+steering+etc..

I can think of several advantages that should more than off-set the above mentioned issues:

Power to weight ratio.
Center of gravity moved rearward.
Less parasitic drag due to only one change in direction of power & no u-joints.
Ability to install and use hydraulic jackplates.

You missed one............

The ability to stand upright with a beer in one hand while wrenching on the motor, not that it is needed that often with a 2 stroke OB, which brings up another one, no oil changes:evilb:

try Checking out :

http://www.armstrongnautical.com/brackets.htm

When my father was looking for a walk around 26-30' fishing boat, we sea-trialed 2 boats that were the same hull - only diff. was the one was rigged single 260 hp I/O and the one he bought was the 225 single OB on the bracket... more use of space in the cockpit, easier to work on and the boat handles like it is 2-4' longer model and jumped on plane quick. They were within a 1-2 mph of each other if I recall correctly as the dealer had them propped ( S/S on OB and alu on the I/O)...and the I/O had tabs (Possible factory option????) - OB boat never had reason to put them on

It is a heavier fishing boat not a high performance hull so I can not say if it is still apples to apples...

Armstrong was really good to deal with regarding technical questions.

Just putting this out there, the Ocean Hawk/Cig Cafe CC and the Cig Decathalon are rigged on brackets - what other boats used these hulls for in I/O applications?

Everyone is making good points...
 

More and more of the OBs are 4 stroke and likely in the not too distant future the selection of 2 stroke OBs might be (even more) extremely limited.

What 4 strokes give up in hole shots, they more than make up in fuel economy and quiet.

As mentioned, mounting brackets are the way to go. They get the prop away from the boat so it can be higher and more control to incrementally raise the prop out of the water and run shallower.

With some pocket configurations the skeg(s) run higher than the keel of the boat. Can cause issues with cavitation on turns, but properly designed it is really not that great of an issue.

Outboards give you alot more flexability, weight savings, and cockpit space. The 2-stroke outboards have become fairly fuel efficient and quiet. They are easier to work on with less grease in the bilge. Some manufacturer have done well with ouboard sportboats. Velocity, Concept and Checkmate to name a few. Active Thunder also finished a new 33 with outboards. The ability to install hyd. jackplates for motor height adjustment and better performance is one big benefit. I'm in the process of renovating a 28' Checkmate with twin outboards. Here's Checkmates latest outboard model:
http://checkmatepowerboats.net/Check...-OBX-2800.html

Hey good advice on this stuff!! My plan would be to install the outboards with a bracket not directly to the transom. I did have a 32 active thunder Face Off sold it two years ago then was told bank took it then went to auction don't know who has it now if anyone knows let me know!! The active thunder was a perfect boat I'm just sick and tired of working on IO's and the fuel it cost to run these boats I know you have to pay to play I understand that but outboards just seem the way to go!! I look at it this way if I blow an outboard I can purchase another about anywhere take it off myself and be on the water the next day!! Also speed is not a big issue with me not anymore anyways. So if I buy a hull that has the motors out of it what would be the steps to putting on outboards with brakets?? Thanks you guys its good to be back on offshoreonly again also any pics would be nice!!

Glass in the transom, hang a bracket, run some wires, and steering, install gages and controls if they are not already there, pretty easy stuff.

bump

I know that Kryptonite built at least one 27' with outboards. It ran about 15mph faster with twin 300's than a 600hp IO version would run. So not too normal, but apparently it works for some hulls.

I wouldnt mind having a nice OB powered boat, no standing on your head in the bilge, instead you are standing in your driveway. Plus, you blow one up, you can get a new powerhead slapped on and be back on the water in a week or less. For a whole lot less money at that.

Take a look at this thread on screamandfly -
http://www.screamandfly.com/showthre...ve-to-Outboard

He's got some very good ideas, will be much stronger then simply closing up the transom, adding knees and bolting on a bracket...

More work but much stronger

You would probably have to add some knees to brace up the transom. Not difficult for an experienced glassman. And we can change out a powerhead and be back on the water in less than an hour. Personally I won't ever own an I/O boat or cat.

Some good ideas any pics out there??

Not always a good thing...
Some boats will porpoise pretty bad when converted to outboards
since they were not designed to have center of gravity that far back.
Just depends on the actual hull it will be done to..

I just finished converting my older 30' v bottom with Merc 300XS. I absolutely love my boat again. I did it for all the reasons mentioned. There are many more. Call me (315)382~8828. Too many things to say here, I hate typing. I have pics that I can email. Thanks
Cary.

Please email me some pics thanks [email protected]

I sent you some pics on your email. Check them out and email or call me. Thanks
Cary

I know everyone says "outboards use less gas" but that's just not always true. If it's a larger heavy boat you need torque to get up and to stay up. That's where the old adage " there's no replacement for displacement" really rings true. So if you put two large outboards on say a 34' Venture you have to stress those power plants to get what you need- if you had two stock 6.2's in the same boat it would ride better( more weight "in" the stern of the boat to mash the waves) and as the motors produce more torque it's going to be a more fuel efficient boat. My buddy's got a 26 Pursuit with a single 250 Yamaha 4 stroke and get's 1.85mpg at cruise. I have a 28' Pantera with twin 6.2's and get 2mpg at cruise... and I'm cruising at 40mph - about 10 mph faster than the Pursuit. Now maybe with blown performance inboards all that changes, but in my opinion on heavy boats, and dealing with stock power, the inboard rules on the efficiency front. I've never seen any actual MPG comparison numbers to disprove that.

That Pursuit is way underpowered w/ a single 250, no wonder he only gets 1.85 mpg. I love my new outboards and would not go back to an I/O, IMO outboards are designed to be in a salt/corrosive enviroment and they are designed to run at high RPM, cant necessarily say the same for I/O's. My last boat was a PQ 280 with a 502 MPI, similar size and weight to my 30 Concept w/ 225 Optis, I havent run any figures yet but I know I get better MPG with the new boat, especially idling around.

I can tell you first hand that my new merc 300XS get double the fuel mileage of my big blocks. The new optimax motors are incredible.

In the same boat???

Michael

Yes, the same boat.

we have a 33FT concept with 300 e-tec's and getting about 1.6 mpg when it had 250 efi's got about .9 mpg

250EFI's are gas hogs, but that is extreme, I get about 1.3 with my single 250 on a 24 pantera

Funny how there's never any real comparison numbers... inboards to outboards. But, is it not true that four stoke outboards came about trying to give us the efficiency of an inboard motor in an outboard package?? That boats need torque, and displacement provides it? On a light boat, yes, but when you put the throttles down and tax a small displacement outboard to push a heavy boat, it sucks down fuel. 29’ Regulator with twin 250 four strokes 1.1 mpg. 28’ Pantera twin 6.2’s 2mpg....

Outboards are easy to work on, less maintenance, cleaner, but in the situation they’re being used in a lot these days they’re not more efficient.