Proline Jetboat to Outboard Conversion.

Bart Hawk

Cadet
Joined
May 29, 2012
Messages
22
Like many others before me the mid 90's jet boats powered by Chrysler's Finest the 90-115hp Mercury/Force Sportjet have become yard art with no other useful purpose.


After neglecting her for a couple of years and almost turning her bow into a tiki bar I've decided to turn her back into a super skinny water fishing machine.

Like many others before me the mid 90's jet boats powered by Chrysler's Finest the 90-115hp Mercury/Force Sportjet have become yard art with no other useful purpose.

After neglecting her for a couple of years and almost turning her bow into a tiki bar I've decided to turn her back into a super skinny water fishing machine.

My main motivation is that she floated in 4" of water with 2 + gear + motor + 10G Gas+ dog.

The plan is:
Pull the motor and housing
Fill the hole with 3/4" Starboard, heavy mesh and resin top and bottom in 2-4 heavy coats.

Reinforce Transom with Starboard, mesh and resin in 3-5 Heavy Coats, and a couple Stainless 1/4" L brackets tied to where powerhead previously lived. (Stringers)
Install Jackplate and new motor, then rigging
Gelcoat Transom, and create Storage / head / cabin in the old engine bay. (It's Huge)

The Questions:
Can I just fill the hole top side and leave the cavity below? (I'm thinking it will decrease my draft and is allot less work) {I've seen twin screws with a similar cavity just before the shafts, it's less pronounced and I'm sure engineered properly}

Will Mesh and Glass over/under 3/4" board to transom be strong enough for a 50-70hp, or should I look more towards a different direction?
POWER: The previous motor was a 90hp jet, I've seen 1 similar conversion with a custom transom outboard bracket and an 85 on it. I want light and like the rest of us as fast as reliably possible.

My main motivation is that she floated in 4" of water with 2 + gear + motor + 10G Gas+ dog.

The plan is:
Pull the motor and housing
Fill the hole with 3/4" Starboard glued in from bottom, heavy mesh and resin top and bottom in 2-4 heavy coats.
Reinforce Transom with Starboard, mesh and resin in 3-5 Heavy Coats, and a couple Stainless 1/4" L brackets tied to where powerhead previously lived. (Stringers)
Install Jackplate and new motor, then rigging
Gelcoat Transom, and create Storage / head / cabin in the old engine bay. (It's Huge)

The Questions:
Can I just fill the hole top side and leave the cavity below? (I'm thinking it will decrease my draft and is allot less work) {I've seen twin screws with a similar cavity just before the shafts, it's less pronounced and I'm sure engineered properly}
Will Mesh and Glass over/under 3/4" board to inside transom be strong enough for a 50-70hp, or should I look more towards a different direction?
POWER: Rated for a 90jet I want light and reliable so I'm thinking 50hp Carborated Yamaha or 07+ Yamaha fourstroke 70+

 

ondarvr

Supreme Mariner
Joined
Apr 6, 2005
Messages
11,527
First start by reading as many other threads here as possible on doing fiberglass work so you will be using the same terminology as everyone else, just makes it easier and less confusing for everyone.

It can be done.

Filling in the tunnel might be the best option, leaving in place may create issues that aren't easy to overcome. It can be difficult to get a prop to work correctly unless the tunnel is designed for it, even then a tunnel that size can cause problems. Leaving as is will increase your draft, filling it will raise the hull in the water. fully equipped and with a motor I don't think you'll be floating in 4" of water though.
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
70,513
Ayuh,.... I agree with ondarvr,... leavin' the tunnel would probably be fatal to the build,...

How 'bout I move this to the Rebuild Restoration forum,....
 

Bart Hawk

Cadet
Joined
May 29, 2012
Messages
22
Made some progress today.

Stripped out all the hardware
Completed a bulk of the prep
Cut and water proofed plugs.
(3/4" PT plywood with 2 coats of 4-1 > 3-1 acetone / resin & 1 coat 1-1.)




 

hadaveha

Petty Officer 1st Class
Joined
Mar 17, 2009
Messages
389
I've seen this done on a few of the Boston whaler rage jet boats. I bet you will have a cool little boat
 

Bart Hawk

Cadet
Joined
May 29, 2012
Messages
22
I used regular marine type resin they sell at major box stores, I only thinned the first couple of coats with Acetone so that it would soak into the wood, it has a final coating of straight resin. It is similar to the whalers but the proline has a huge compartment in the aft that I am still deciding what to do with.
 

jbcurt00

Moderator
Staff member
Joined
Oct 25, 2011
Messages
24,863
I used regular marine type resin they sell at major box stores, I only thinned the first couple of coats with Acetone so that it would soak into the wood, it has a final coating of straight resin.
EPOXY

or

Polyester resin?

Ondarvr's advice is the same no matter which resin you used, don't thin the resin, but if poly it also needs to have fiberglass cloth/mat.
 

ondarvr

Supreme Mariner
Joined
Apr 6, 2005
Messages
11,527
Many or resins sold in the big box stores contain wax to make them cure tack free, you DO NOT want waxed resin, so check it.

Thinning resin turns it into junk.
 
Last edited:

Woodonglass

Supreme Mariner
Joined
Dec 29, 2009
Messages
25,924
You will be applying another full strength coat of resin and a layer of Chopped strand mat to cover the wood...right???
 

Bart Hawk

Cadet
Joined
May 29, 2012
Messages
22
Got the plugs installed and another coat of glass laid today. Hopefully I'll be able to bully through it before the heat hits in FL
Scrapped the plug with thinned resin, yes I am laying up mat with resin. (Marine Specific Resin)

 
Last edited:
Top