Outboard Questions

grundasaurus · Post by **grundasaurus** » Fri Jun 12, 2020 1:48 pm

Hello all, We've gotten bored in quarantine and have been building a bolger diablo (with materials from boatbuildercentral), and we're trying to figure out what our options are for power. We've redesigned the structure significantly and have built a full motorwell for added strength. We've also been using biaxial rather than the woven tape called for in the book. The plans call for 25hp max, but I've got a 1982 2 cyl johnson 60 that seems like it would just be perfectly excessive. I'm leaning towards the bigger motor especially cause it only weighs about 180 pounds compared to the 110 pounds of the 25. Would this be absolutely mental or reasonably doable? I'll attach photos of the structural changes soon. The boat will also have a center console for added comfort and balance. It will also have full length skeg glassed in to keep the bottom stiff at speed.

Capt UB · Post by **Capt UB** » Fri Jun 12, 2020 2:50 pm

grundasaurus wrote: ↑Fri Jun 12, 2020 1:48 pm Hello all, We've gotten bored in quarantine and have been building a bolger diablo (with materials from boatbuildercentral), and we're trying to figure out what our options are for power. We've redesigned the structure significantly and have built a full motorwell for added strength. We've also been using biaxial rather than the woven tape called for in the book. The plans call for 25hp max, but I've got a 1982 2 cyl johnson 60 that seems like it would just be perfectly excessive. I'm leaning towards the bigger motor especially cause it only weighs about 180 pounds compared to the 110 pounds of the 25. Would this be absolutely mental or reasonably doable? I'll attach photos of the structural changes soon. The boat will also have a center console for added comfort and balance. It will also have full length skeg glassed in to keep the bottom stiff at speed.

That a beautiful design. The videos show her flying with the smaller OB's. On JM's designs, USCG says one thing, the designer is keeping you safe. I have a FS14 with a 9.8 4 stroke, (Outboard recommended/USCG 6 to 15 HP/25 HP) very happy with the speed, could use a 20 + with us BOOMERS onboard

Look up some the 16 cc boats here and look at their study plans to match your hull and weight layout. Should give you an idea about hp and weight.
Post if you can some photo's.

Build On...
Bob

pee wee · Post by **pee wee** » Sat Jun 13, 2020 10:00 am

I think the biggest problem with going to more horsepower than the boat was designed for is somebody will at some time use that extra power, putting strains on the boat it was not designed to withstand. The additional weight is a secondary concern.

grundasaurus · Post by **grundasaurus** » Sat Jun 13, 2020 12:26 pm

Here are some photos showing what we've done so far, the front two frames were moved forward to create a large casting deck, and the rear frame was moved backwards to create the motorwell. This obviously leaves a large unsupported space in the middle. I plan to create two more frames that will be cut down to keep three inches of frame all the way around the boat, I'm then going to reinforce these with some longitudinal runners which will act a bit like stringers and allow me to build a slatted deck to keep your feet dry. I'm planning on running the skeg all the way along the bottom to also add reinforcement, the draft will suffer a bit but this boat will seldom ever be running in shallow water. We're very open to suggestions on how to reinforce things better though.

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