Whaler Central - Boston Whaler Boat Information and Photos

Posted by visket on 10/07/18 - 10:21 PM

Hi Folks -

New member - first post. Might be my last!

I bought Mighty Squirt (1984 13SS) new. Have legendary stories.

I have bigger boats now (notice plural reference - 3 total), and instead of selling Mighty Squirt (with a perfectly maintained 2008 Merc 40 Four Stroke), I was thinking of putting a Rotax 785 Jet package in it (from a 2000-ish Sea-Doo GTX). This motor produces 100+HP, which, combined with a Jet pump, would net perhaps 75HP of thrust. Sounds dangerous, but with the maximum 6 person/950lb limit, I could take a crew of 1 adult and 3 grandkids tubing a whole lot easier!

Please don't judge me. The selling prices of used 1984 13SS is less than I can sell the Merc 40 for.

I measured the distance from the transom of the GTX to the front of the 785 at 36". I measured the distance from the transom of Mighty Squirt to the aft of the seat locker at 37". There is room, without too much interior cutting. So it is looking like it COULD work....

I am asking:

1) Has anyone performed an "outboard-to-jet" conversion on any of the Super Sport models?
2) In general, what "Gotcha's" should I be looking for? Cavitation in turns, for instance?
3) I would install a "low speed" (hi pulling power) impeller so I could take the grandkids on the towed inflatables.
4) This would allow Mighty Squirt to do "river runs" from Laughlin, NV to Lake Havasu, AZ on the unpredictable depth of the Colorado River without worrying as much about prop/skeg damage.

What considerations should I think of (other than re-sale price or that 2-strokes are being banned)?

I don't know what I don't know - to phrase it.

Thanks -

Mike

Posted by butchdavis on 10/08/18 - 7:04 AM

Mike,

I have mixed views. It's a little like taking an original Model A Roadster and turning it into a hot rod. Almost sacreligous. OTOH I've always loved hot rods.

I think I would try to find a cheap rough hull and experiment on it. Then, if it didn't work out it would a small loss and if it does you can reconfigure the rough hull into a family friendly sports boat and you would still have a family heirloom classic.

Posted by visket on 10/08/18 - 8:06 AM

Now there's an idea I didn't think of. A great idea. I'm not in any hurry, so I'll keep my eye out for a similar hull.

Yep - it would be a hot rod. I have had it to 35mph in the past (with the original Merc 35), which is about as fast as I would ever want to take it. I would try to "gear" the jet to that range, hopefully giving me a strong hole shot.

I also realize it would be noisy. The current Merc 40 Four Stroke is so quiet, it's easy to speak to the crew. I think this is my primary concern - making an engine bay that muffles the sound adequately.

I think the test hull would allow some prototyping for both gearing and sound control.

Thanks Butch -

Mike

Posted by Weatherly on 10/08/18 - 9:55 AM

Take a look at the wood locating diagram for a 1984 Boston Whaler 13 hull (downloads section of this website). The plywood located in the cockpit is for fastening console floor cleats, battery straps, an other needed light duty assessories. There are no stringers in the hull. The 13 hull was designed only for outboard use mounted on the transom. What are the specs/weight of a Rotax 785 Jet engine? You will need to install supports to mount such an engine. I would advise again cutting into the cockpit floor, compromising the unibond-constructed hull because you will lose sheer strength. I like Butch's suggestion to find a beater hull and experiment with your project concept.

Posted by visket on 10/08/18 - 6:07 PM

So I'm not sure of the weight of the Rotax 785. They were rated at 100hp, and they are twin cylinder 2-strokes. The jet boat mechanic in town usually has one or two 785s in various states of assembly, so we should be able to guestimate a weight for the motor / pump / exhaust, etc... I am thinking less than 200lbs, easily. Which is what the original Merc 35 weighed.

The jet boat mechanic also does fiberglass (he fixes the rental jet skis/boats in town), so I'm confident we can design the braces.

Still - the idea of using a rough hull is what will bring this project together.

Oldboats - this whole project will come to a stop if I need to cut into the locker or rear seat, so I'm letting you down up front - no furniture for you! I'll keep you in mind if I find a rough boat with decent furniture, though.

Mike