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Flats Flyer Modification

Posted: Thu Feb 01, 2018 6:01 pm
by Conrad
I want to eliminate the motorwell and hook a jack plate directly to the transom. I was thinking of bringing the 2x6 transom cross member up to the top, but now I’m wondering if the transom knee should just go all the way concern is the strength of the transom. Should I thicken it as well or should the double ply be enough to handle the jackplate? Should the center 2x6 be maintained?

Re: Flats Flyer Modification

Posted: Sat Feb 03, 2018 8:55 pm
by Kevin Morin
Conrad, I'm not replying as a wooden boat builder but as someone who's spent a bit of time with that design.

I'd note for your review that the design has some of the two sponsons reaching aft the engine mount and I think you're referring to that arrangement as a "motorwell" ? In my (confined to the Pacific NW) terminology; engine wells have a skiff stern aft the well but the bottom of a planing skiff with well would have similar waterplane in Plan View.

But regardless of the terminology we may be using, my impression from doing a weight and balance of the Flats Flyer is; the two sponsons' extension aft the engine mount; provide a two very significant design features I'd caution you to consider in this design.

#1 at rest, the two sponsons add buoyancy moment AFT the engine mass- so the hull sits more level/less bow up at rest. Depending on the engine and other loads- this means the engine at the stern will squat the hull downward at the stern and leave her to sit pitched up by the bow.

As I understand this hull's purpose in use- a level casting platform is key? The two sponsons' help keep a heavy engine from leaving this hull from 'sinking' by the stern while at rest.

#2 Planing thrust and running trim. I'm sure you're aware of the effect of trim planes of the type that are parallel to the running waterline and pushed downward aft the transom? Well, the two sponsons' planing bottoms AFT the engine thrust work in a similar, if less dynamic, manner. They are fixed, BuT their contribution to pitch is AFT of the engine thrust- so they work to keep the bow pitch lower.

These two hull/sponson extension planes act to keep the bow 'flat' or not as pitched up as might be the case of a similar sized flat bottoms skiff with a transom mounted engine running in similar conditions.

If you locate the engine aft- at the sponsons' after most ends- you will experience more bow-up pitch than a comparable Flat's Flyer if built to the design with the engine located forward of the aft most ends of the sponsons.

Just a few remarks because at one time I'd looked fairly closely at this hull design and done some design exercises modeling of this hull. I'm confident you can overcome both of the performance results I'm noting but- please realize these factors in your planning.

FULL DISCLOSURE: I have never built or seen a Flats Flyer in person, I have only been exposed to this design from a review of the Flyer's design here and cannot speak from any first hand Flyer experience. I have built outboard powered skiffs both with transom mounted engines and those mounted in a well.

Kevin Morin
Kenai, AK

Re: Flats Flyer Modification

Posted: Mon Feb 05, 2018 2:24 pm
by Conrad