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Discussion Starter #1
Hello,
There is nothing like designing and building a boat (maybe an airplane) it has a function and personality and a life of sorts and its all you.

My name is John Barrett and I live In Houston TX. I am in the middle of a design build of a small motorized one person skiff. The boat is 11' long and 48" wide, shaping an EPS/XPS foam core and am about 2/3 of the way through shaping. It will be skinned with a Basalt/Innegra and fiberglass cloth in Epoxy resin.
Design criteria for this boat are Light Weight, less than 70 lb (I will car-top it), shape optimized for stability and motoring (not a paddle board with a motor). Max buoyancy outboard, semi cat shape with a narrow center sponson from bow to 2/3 aft. The outside sponsons end into a planing pad aft. This gives the bow a tri-hull look and the stern is low and flat. Boat will be self bailing, 15" tall at the bow and tapering down to 7" at the stern.
I was originally going to make it a split tail with inset motor but have another idea to inset motor forward of the stern and not split the tail. Boat will float in about 3" fully loaded and I am planning to be able to raise the motor for low speeds in water less than 10".
I am planning on using a 6hp Tohatsu but have been seriously considering a 3.5. I expect about 16 mph out of the 6 but if I could get 13 mph out of the 3.5 I would do it. The prop rpm calculations for the 3.5 say it can but I am worried that slippage might be too high with the lower thrust 3.5 and my 4' beam and it mightl be too slow. The hull could carry a 10 hp according to Coast Guard criteria but since I'm car-topping and a 9.9 weighs 90 lbs, cant lug that around.
I am a wade fisherman, I am building this boat to mostly get me to my wade fishing spots, plan to launch less than 5 miles from where I am going to fish and get there in less that 30 min. Kayaks are just too limiting in range and they are hard to fish out of I couldn't sit in one for a 7 or 8hr day. When I do fish off of this boat I will be standing, rarely sitting. When I wade I carry or pull all of my gear with me so I will not carry a lot of extra tackle or rods. Wading makes you very conscious of carrying what you really need.
I expect to float the blank in a couple of weeks, its a lot easier to change things before I glass it. LOL I will post pics of the blank when a take it out of the shop.

Thanks, I welcome input and am open to critique.
 

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Brandon, FL
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10,094 Posts
Check out the thread building something really shallow, it will give you ideas. Also there is the solo skiff for ideas as well.
 

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I Love microskiff.com!
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Sounds like a cool build. The real problem with the smaller motors on a planing hull IMO is the lack of prop options. It looks like there is an aluminum prop available rather than the factory plastic option, a good shop might be able to work some magic on it.
 

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Discussion Starter #6
Sounds like a cool build. The real problem with the smaller motors on a planing hull IMO is the lack of prop options. It looks like there is an aluminum prop available rather than the factory plastic option, a good shop might be able to work some magic on it.
The Tohatsu 6 comes with an aluminum prop and the dealer said Tohatsu offers a selection of props. Just not sure how much could be gained by tweaking the prop in this case. Looking at potential speed using a prop calculator and the specs on the factory prop it has an absolute max speed of right at 19mph but very well could be around 16mph. If I'm in that area that's fine, I just don't want a slug that barely planes. Total weight will be under 400 lbs. hull, me, motor gear, ice chest etc. and there is plenty of planing surface. You can also do a lot by moving your weight around to get on plane and adjust hull trim. I will be half of the weight + of this whole loaded rig. A tiny boat like this is so much more sensitive to weight placement than even a little 16 footer with 2 guys and gear and 30 hp motor. If I changed props or cupped the prop or both I would guess it would be hard to get more than 2mph more out of it. It seems there isn't that much thrust potential there to work with. But there is a lot of guessing involved. LOL
 

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I Love microskiff.com!
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Kind of like a scooter- I like the concept. Will it handle two folks?
 

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Brandon, FL
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I think you have high hopes for 13 from a 3.5.

The L/W ratio does not lend itself to be a fast boat by design. A 4x would be a fast hull, your is 2.75. 4X for 48" is 16'; for 11' is 33". Surfboard sized.

Throw up some drawings.
 

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BBA Counselor
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I agree with DuckNut. At 48" she is short and fat. Good for stability, but not so much for efficiency or handling. That's also a lot of wetted surface causing drag to overcome. Most Jon boats that size are around 36".
Not saying it can't be fun and functional, but 13 mph will be hard to achieve with a 3.5hp, and she may want to crab a bit so you gotta design and ballance to avoid that.

Let's see some concepts.
 
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