Inboard to Outboard conversion

[pellsweb]

I have just bought a 14ft speedboat which has been totally stripped out. the hull is sound as is the body, what i would like advice on is where the prop shaft exit hole is, what would be the best way to cover this, i was going for expand foam trimmed and fibre glassed over in multiple layers, will this work and will the boat be seaworthy for pleasure trips with this kind of fix.

thankyou

 

[smokeonthewater]

Re: Inboard to Outboard conversion

instead of reposting just hold on for a mod to move it for ya..... won't take long...... also do some searching. there are bunches of threads about this subject

 

[DukesFin]

Re: Inboard to Outboard conversion

Prop shaft holes are usually for inboards, so I'm assuming that's what it is...

There will be plenty of responses, but in short answer, YES, it can be done and you're on the right track with multiple layers of fiberglass but...

You'll need multiple layers from both inside and outside and both sides beveled or "scalloped" to take the new layers inside and out. You'll want layers of biaxial, cloth and probably some mat thrown in as well.

The bigger question/issue is how the hull was designed. It was designed for the weight of the motor to be amidships (or close to it). When you move a motor to the transom, it will want to squat, not to mention the transom work you're going to have to do so you can mount an outboard on it. You may decide to use a motor bracket though. In that case, your center of gravity is moving even further back, thus the "squatting" issue becomes bigger...

Like I said, more will chime in on this, but there are some that can do just about anything to a boat because they just "want to" and others that will tell you to sell what you've got and put that money towards the boat you really want.

Good luck though!

 

[pellsweb]

Re: Inboard to Outboard conversion

hi and thanks for the responses,

the foam will sit in a well of about 4 x 2 inches and encased within the fibre glass, or at least this was my thinking.

this is my first boat project so im after any useful advice.

as for the weight issues and stability how can i realistically gain weight in the front with a good balance so that the boat sits nice in the water.

 

[Mark_VTfisherman]

Re: Inboard to Outboard conversion

...as for the weight issues and stability how can i realistically gain weight in the front with a good balance so that the boat sits nice in the water.

The way the boat sits in the water is the least of your problems... First is the engineering of the hull- the transom specifically. I/Os and inboard hulls don't have the transom design and strength to hang an outboard. This will need to be addressed first.

Hull balance is another matter entirely. On a 14' boat the hull may not be differently shaped than an outboard hull. That will need to be taken care of later- after you rebuild the transom appropriately for an outboard.

 

[pellsweb]

Re: Inboard to Outboard conversion

mark vtfisherman

thanks for your comments, as i said before this is a complete first for me, i have never rebuilt or redesigned a boat before do you have any suggestions on stregnthening the transom, any suggestions are welcome.

my uncle has done a similar thing with his boat but he is currently at sea for 3 mths so my source of information has gone.

 

[pellsweb]

Re: Inboard to Outboard conversion

http://www.pellsweb-sol.co.uk/boat.html

here is a picture of the boat so you may get a better idea of what im dealing with.

 

[Bob_VT]

Re: Inboard to Outboard conversion

Welcome to iboats!

I will move this to the restoration section. Please post pictures of what you have now and we will try to help. Normally an outboard bracket will help with your problem however, MOST people who have tried the conversion have not been happy with the results.

The top three threads in this section will help you with posting your pictures at a 640 x 480 size. http://forums.iboats.com/forumdisplay.php?f=32

 

[DukesFin]

Re: Inboard to Outboard conversion

Before I respond again, I just have to ask...

Why are you going to spend the HUGE amount of time and quite a large chunk of change on such a project when it makes more sense to get rid of the boat you have and buy one that you want? Again, I'm not saying it can't be done, but you're trying to re-invent the wheel by doing this and anyone considering such a project needs to be sure they understand WHY they are doing it, then be sure they understand what a large financial investment it is going to be.

That being said/asked...

Most outboard motor transoms are constructed of (going in "layers" from the outside of the transom into the bilge area):

Outer skin of fiberglass
2 layers of 3/4" marine plywood bonded together with resin
Inner fiberglass skin filleted into the inner hull on sides and bottom
"Transom Knees" that help distribute the force of the outboard into the stringers of the boat.

What you are probably looking at is removing all of your current drive system, removing the cap/deck of the boat (at least a good portion of it so you can do the transom/stringer work). Cutting the transom down to accomodate what will probably be a 25" shaft outboard and a LOT of fiberglass work (I'm leaving out how much transom work because I have no idea what yours looks like...

If I were you, I'd go onto the boat restoration forum here at iboats and take a look at some of the projects there to give you an idea of how both styles of boats' transoms are done and see if changing yours over is a project you want to take on.

I don't know your uncle and maybe he did a fine job, but... If it wasn't done "right", I wouldn't set foot in it! If your uncle's project didn't take long at all, didn't cost much at all and was easy, I can bet it wasn't done well. I'm not trying to put anyone down or anything but there is no way around spending some coin and a lot of time on this project. Any other way and it's a catastrophe just waiting to happen... Either a motor coming off the transom going/trailering down the road, sitting at the dock or while underway in the water. None of these is responsible.

I think if you just looked at how involved FIXING a boat's transom is, then thought about how much more involved re-designing one is, it will give you a better perspective on this.

Keep the questions coming though. I'm not trying to discourage you, but only trying to be sure you fully understand what it is you are trying to do! If you take on the project, I can't wait to see your posts with pictures!

 

[pellsweb]

Re: Inboard to Outboard conversion

im beginning to feel a bit discouraged now, but im going to still try and work it out.

 

[DukesFin]

Re: Inboard to Outboard conversion

Oh, don't be discouraged... Take a look (it will take HOURS to) at this project... One of the "hall of famers" on this site: http://forums.iboats.com/showthread.php?t=234392

So, if anyone tells you it just can't be done, let THAT project tell you that IT CAN!!!! It's really about what you want and why, not "if it can be done"!!!

Seriously though, look at that project... EVERY PAGE of it and you will have a great deal of understanding of every facet of fiberglass boat restoration, building and transformation. It contains volumes of information helpful to anyone doing what you want to, or someone just wanting to simply repair a scratch!!!!

 

[erikgreen]

Re: Inboard to Outboard conversion

im beginning to feel a bit discouraged now, but im going to still try and work it out.

I think that boat looks great - should be a lot of fun to drive in the right conditions.

But I wouldn't try to put an outboard on it. That boat is designed for an inboard engine, and redesign for an outboard would be a major task if it's even possible. I can't see the transom in the pic, but I think it's probably minimally constructed, and to hold an outboard you'd need not only to replace it but to reinforce it with knees going to the lower hull, to stringers that may not be there, and as others have mentioned add a lot of weight.

Weight and balance would be the biggest problem. This hull has not much buoyancy in the rear compared to farther forward, so putting the weight of an outboard back there will require ballast (think lead or concrete) far forward to make it sit level, and this will reduce the weight the boat can carry as well as make it harder to handle... I'm guessing you probably want to have a fast, light boat for fun driving, so that's not a great idea.

But if you can re-do the inboard drive, this would be a fun boat. Is there a reason you don't want to do that?

Erik

 

[system-f]

Re: Inboard to Outboard conversion

I think that boat looks great - should be a lot of fun to drive in the right conditions.

But I wouldn't try to put an outboard on it. That boat is designed for an inboard engine, and redesign for an outboard would be a major task if it's even possible. I can't see the transom in the pic, but I think it's probably minimally constructed, and to hold an outboard you'd need not only to replace it but to reinforce it with knees going to the lower hull, to stringers that may not be there, and as others have mentioned add a lot of weight.

Weight and balance would be the biggest problem. This hull has not much buoyancy in the rear compared to farther forward, so putting the weight of an outboard back there will require ballast (think lead or concrete) far forward to make it sit level, and this will reduce the weight the boat can carry as well as make it harder to handle... I'm guessing you probably want to have a fast, light boat for fun driving, so that's not a great idea.

But if you can re-do the inboard drive, this would be a fun boat. Is there a reason you don't want to do that?

Exactly. Inboard boats are so cool, why wouldn't you try to reconstruct the factory drivetrain?

 

[funk6294]

Re: Inboard to Outboard conversion

That is a cool looking boat and I can see why you would want to turn it into a project!!! Post up some more pics so we can all get a better look at it...

 

[pellsweb]

Re: Inboard to Outboard conversion

In repsonse to all who have replied,

i havent kept as an inboard because there was no motor with the boat, i simply want a boat that myself and the other half can go out in the bay and fish for a few hours, im not after speed or craziness, just some pottering around.

The motor im putting on this is only 5 hp mariner.

like i said i am only interested in floating about with a line in my hand for fish, the transom on this boat is slightly wedged shaped BUT i have had som advice of how to fit an outboard with tiller extension, but as has already been stated weight and true bouyancy will be the issue.

Thanks for all posts and i have taken all into consideration, however not meaning to sound like a know all i beleive that anything is possible so i can only give it a go.

phil

 

[Numlaar]

Re: Inboard to Outboard conversion

If you are only sticking a 5hp OB on that boat, I dont think weight or transom stress is going to be an issue...

I think most people here assumed you were trying to re-power it with an OB appropriate for the size of the boat....

That being said, you will definitely be puttering around with that 5hp on there hehe...

As for the hole, the layered matt/resin approach (as a few have suggested) is going to be your best bet for strength.

Good luck!

 

[pellsweb]

Re: Inboard to Outboard conversion

numlar

thanks for that response, i feel a bit better now.

I am going to reinforce the transom anyway to allow for a bigger motor in the future I have access to a 25hp motor that is going to be the test motor for weight and stress on the transom, i cant see me going any higher than that in the near future, i think ill stick with the baby for one season and see how things fair out.

I am going to create a website showing progress of the boat so ill post that as soon as I have.

Im going to enjoy this project, as i stated before its a first time for me but its also a challenge so im gonna rise to it.

 

[DukesFin]

Re: Inboard to Outboard conversion

I've heard there is already a website where people document boat projects...

If only I could remember that website... Hmmm....

;-)

 

[pellsweb]

Re: Inboard to Outboard conversion

im a web designer so i can actually do it myself.

if you remember the site then please let me know

 

[Robert4Winns]

Re: Inboard to Outboard conversion

im a web designer so i can actually do it myself.

if you remember the site then please let me know

I think you are on it right now.