Tell me why this won't work.

[lewisboats]

10.5 ft LOA
52.5" beam
375 lbs pictured displacement (fresh water) at 6.3" draft
Sail area to 80 sf (balanced lug or other low aspect sail)
Horsepower to 7.5
7 ft oars

Notice the chine reverses at the bow and stern. The reason there is a belly in the chine is to increase weight carrying capacity or overall displacement while keeping the ends where they are.
At the bow this is to help with the entry angle...45 degrees as shown, while allowing for increasing buoyancy as the bow plunges.
At the stern...this allows for minimal transom immersion for sailing or rowing while at the same time providing maximum lift to begin as the boat rotates just a couple of degrees when using the motor. The buttocks lines are virtually straight to slightly hooked. I expect the boat to plane with a motor and not have the bow pointed nearly so high as it would with conventional aft rocker and a transom that is completely out of the water.
Weight placement will be quite important...it would require the majority of the moveable mass to be centered at right about the 5 ft point forward of the transom for optimal performance. Coincidentally, this is also just about the best place for a single rower (about 14" forward of the max beam) and also a nice comfy distance to helm the tiller when sailing. For maximum performance this is a 1 man boat...BUT...it can carry up to 3 if you want to use it like a barge...maximum displacement is 675 lbs. This means it would be a good small lake/big pond fishing boat for 2 men and gear. It would also be a good boat for a couple of kids to sail or row around in.

So...tell me why my set of compromises wouldn't produce a boat that could do all three well enough to be worth building. It won't sail as well as a pure sailboat (85-90% though), it won't row as well as a pure rowboat (but as well as or better than most pram dinghys) and it won't motor as well as a pure motor boat (but probably better than a 10 ft johnboat...it won't trip)

 

[hoytedow]

It sure looks like it would get you there.

 

[nukisen]

I don´t see the centerboard for sailing. Else, why shouldn´t it work?

 

[eyschulman]

Look at Gig harbor boat works 15 ft lobster model. row-sail-power same set of objectives you are looking for. they also have smaller designs.

 

[hoytedow]

No mast either but the hull looks ok.

 

[lumberjack_jeff]

I like it... a nice two-sheet boat.

Could you please post a photo with development turned on? In a small boat such as this, I suspect that the bottom panels experience some nontrivial twisting.

 

[lewisboats]

Here is the "Developability Check"...the only spot that may be a problem is the forefoot or chin if you will. Freeship was designed with Steel panels in mind and it is a bit stringent in it developments. This shape can be gotten out of 6 mm ply or very close to it. I have done it before.

Here is Fisher10 developability check

Fisher10

Fisher10 bottom butterflied

I haven't done sailplan or foils yet but it would be spec'd for a dagger board and a balanced lug of around 75-80 sf. 2 positions for the rudder...centered and offset. Offset so that a motor can be hung...also offset, to be used in a fixed position and steered with the rudder. The motor can also be center mounted and used for straight motoring and unlocked for tiller steering with an extension.

(Maybe I should call it Wiggles...for the wiggly chine!)

 

[nukisen]

Wow!
Good luck Lewis.
This will be great.
I do allready like this little boat.

 

[lumberjack_jeff]

I agree Steve, Now seeing the modest red area, it'll be fine. My driftboat was more severe than that with 12mm. I was concerned that the twist at station 8 and 9 might be tight, but it appears to be okay.

Assembly tip: use a pneumatic stapler instead of stitches. In 6mm ply even t50 staples will hold the chines together adequately. Maybe put a few (3-4) stitches in last 12" of bow and stern, stapling is much faster, much easier and makes filleting the inside of the chines much better.

 

[lewisboats]

I usually use 4" wire ties...with a 3/32 hole and the ties stay in the fillets. I just nip the rest outside off flush with the plywood. The reason I like the ties is I can adjust the tension to help square things up. I start with a slightly loose loop and get the edges just how I like them then gently tighten up. I usually only need 1 tie per foot until it gets to a tougher curve then I go to 6" or even 3" apart. I can make a bigger hole and double up too if the pressure is a lot.

 

[rwatson]

Sam Devlin and others don't recommend leaving the wire in the fillets. Evidently they work their way out over time, and promote moisture ingress as they rust.

I find plastic cable ties pretty good, but wire is great in places where you need to be able to do a bit of custom bending to hold a tricky bit together.

 

[lewisboats]

These are plastic ties...cable ties. I don't use wire as I have been bitten (cut) too often and in my experience...copper breaks too easily and steel is just a pain in the...well you get the idea.

 

[lumberjack_jeff]

I've used steel electric fence wire, aluminum fence wire (wholly unsatisfactory), cable ties, and staples.

Except for the high tension areas in the ends where we use a couple of stitches, staples work best for us, and by far cheapest and fastest. T50 works best for 6mm, 7/16 crown construction staples for anything thicker. If you choose an appropriate staple height, it won't upset the inside of the chine making filleting a breeze.

It's good to have a helping hand if you're bending/stapling 9mm or thicker, but Steve's boat should staple together singlehanded in about a 30 minutes.

Definitely don't leave wires or staples in the boat (although they make monel staples if you insist). If the glue prevents easy extraction of them, heat the steel with a soldering iron, and the wire will pull out easily.

Back to topic: I like your design Steve, I think the main potential annoyance will be the tendency to squat when under power, but as you note, it's a compromise design, and with 7.5hp, it doesn't sound like you're expecting it to plane. I think it'll be a nice little rowing sailboat that will accept a small outboard.

 

[philSweet]

7 hp ?? The first boat won't plane very well and won't like 7hp one bit. 2-4 hp would be plenty.

I think 6.5 foot oars (or even 6'ers) would do better. I think you would need to raise the oarlocks to get 7'ers to work. And they would have to be at different heights to allow crossed hands rowing. (I don't think you want to go beyond the 2:1 outboard:inboard ratio on this boat.

 

[Collin]

+hollow mast and balanced lug and you'll be a happy sailor.