1977 15' Imperial Tri-hull Restore / Jetski Conversion

[huntersirg]

So I took the plunge and bought my first boat! It's a 15' 1977 Imperial Fiberglass Tri (says VS on title??) pretty much just a hull.

I run a kiteboarding school in Clearwater, FL and on days when we have offshore wind it's necessary for me to get gear, clients and a jetski out to the barrier islands. So I've been looking for a boat to convert into a light weight shuttlecraft that the ski will "plug" into and finally found one light enough with part of the work done.

The older gentleman that had it before completely striped it and dug out all the waterlogged foam. He told me he cut a bunch of the cap off to keep the weight down. Then just stopped there tossed in some slightly painted ply and rocked a 8hp with the stringers completely rotted out. :facepalm: Hull still seems solid but I think this boat design got a lot of strength from the foam. Looks like the cap was removed then used some cheap wood to hold the rivits and half glassed???? (see pics) Also I'm going to build a boat dolly to try and straiten this boat before glassing the stringer any suggestions on how to check that its strait and keep it that way when cutting parts out?

For the jetski docking my plan is to cut the transom out and glass a new one about 5 ft towards the the bow. then I'll build a wood frame/rails that the ski will slide into. Basically like shortening the hull sectioning it off from the back U section for the ski. Hope that makes sense I have buddy that may do a rendering for me to help visualize the end result befor cutting to much.

Any idea on how the stringers were originally?
and
Where should I start first?

a) Remove cap, start work on the cut out for the ski.
b) Leave cap, just epoxy exposed wood holding cap on
C) What would you do?

Sorry for so many questions!
and
Thanks for any help on this, I will keep this updated with photos and video. If it wasn't for great forums like this one and helpful souls I wouldn't even attempt this!

 

[Woodonglass]

Re: 1977 15' Imperial Tri-hull Restore / Jetski Conversion

That hull was a single stringer hull that DID rely heavily on the injected foam for structural support. To do what you are proposing, I'd recommend fabrication several bulkheads port to starboard and then adding the pourable foam as well. The rear Jet Ski dock is another matter totally. I'd prolly try to design it similar to a 4 bunk trailer.

 

[sphelps]

Re: 1977 15' Imperial Tri-hull Restore / Jetski Conversion

So I am assuming that the plan is to use the jet ski to power the boat ? The hull capable of holding a few students and gear and just kinda push it around ? If so that is a totally kool idea !

 

[jbcurt00]

Re: 1977 15' Imperial Tri-hull Restore / Jetski Conversion

Was the 1977 Imperial an air-slot type hull?

Looks more Airslot like a Wellcraft then typical tri-hull:

1975 Wellcraft:

If so, it may prove to be an even better choice for your intended purpose. Better 'flat/wide' & stable platform then a Semi/Deep V. Better big water wave & wake crossing then a tri-hull that might tend to try to pound your kidneys outta your lower half....

Sounds challenging & interesting, but may be entirely possible....

What year & make ski?

Any chance you have access to a current docking model Jetski setup, to see what's the 'keeper/interlock' system on those. Or the support/rail system...

WOG's on point w/ the additional bulkheads & foam. The foam & bulkheads should help prevent torsional twist, which could be significant when you cut out 5ft along the keel, wide enough to accommodate a jetski, on a 15ft boat....

For a bunk style support system, you might consider those high tech eze slide polymer (??) bunk material:

But I guess that might make it harder to keep the 'skiff' & the ski attached to each other....

Tagging along...

 

[huntersirg]

Re: 1977 15' Imperial Tri-hull Restore / Jetski Conversion

Thanks woodonglass and JB.
Recruited some great helpers lol

I'm really liking this hull design more and more, should handle the 2' chop we get in the intercoastal channels when its blowing 20 knots! Made a boat dolly with 4x4s bolted together I'll post pics and a how to if anyone wants it. I went ahead and ordered some glass and epoxy. Help has been nice but spent most my time helping and guiding them, one I didn't mind doing this with.


Progress so far

Dolly made

Stringer cut and cleaned out.

Boat cleaned and packed full of some weight and going to drop it in the water and check for leaks this evening.

Fiber and epoxy ordered

Materials list so far
12oz 38" 20 yards $64
6oz 10" 50 yards $38
3.22oz 50" 20 yards $55
Thayercraft.net
Pretty great prices I've ordered fiberglass for building my kite and surfboards and they are hit or miss but if there's a problem (most the time its wrinkles caused by shipping) they have taken care of it in the past and sent a replacement roll.

Uscomposite Epoxy one 3 gal kit and a 1.5 kit should be enough if not I have some resin research epoxy to finish it.
1/4 chop
Cabosil
4lbs foam kit

Found some 3/4" marine ply at homedepot of all places but it was a special order that someone hasn't picked up I'll find out tomorrow if I can buy a piece guy said he'd cut me a deal since they may have to eat it. Want to go with 3/8 decking and glass both sides with the 3.2oz trying to keep the weight down.

Trailer needs work and I want to have it sitting pretty straight when I glass everything together so planning on getting it on the dolly tonight, just worried about lifting it off the trailer with no stringer. Going to drop the front of the trailer down to block off the stern with cinders and 4x4s then run a tow strap 5-6ft from the bow with two ratchets on eachside to a balcony support beam should I try and put some 4x4 under the strap to spread the load? Stripped out right now its pretty light I can lift the bow and stern by myself.... a few inches.

Stay tuned.