Sled Boat Bow rise

Is there a formula or rule to figure bow rise from the bottom of the v ? I'm getting ready to build a sled boat and have made several wood templates cut on my cnc. I know that the bottom sheet is 78 inches wide has a 15 degree dead rise which is about 9.75 inches in height with 30 inch sides which should be around 38 inch overall height. and it has a 102 width beam. the boat is twenty feet long and the start of the curve or tangent point is about 9.5 to 10 feet , I have measured lots of boats and this value varies. I'm trying to determine how much radius to put into the bottom to achieve this. here are some pictures of what I'm trying to achieve. Thanks !

 

No.
It is usually driven by the fairness required for the lines running fwd, the material you're building with as well as fashion and needed reserve bouncy, speed to name a few.

 

The boat is well on the way to being built, and you are puzzling over shapes and dimensions ? I don't understand what you are referring to, using the term radius.

 

Thanks for the reply, all that seams complicated.

Thats not my boat thats just a picture of what I'm trying to achieve, the plywood laying flat on the work bench with the inside radius is what causes the bow to rise thats the radius I'm looking for without cutting more samples if that makes sense.

 

You are in possession of plans of some kind ?

 

No just designing it on my own, winging it if you will.

 

Sounds a bit fraught, what is the intended use ? Type of power ?

 

fishing boat for bay use and possibly ocean when it lays down flat, 150 hp Yamaha prop with 9.9 kicker. very common here in the pacific northwest.

 

This is awesome. I’m kinda doing the same thing. Modified V. I was playing with the radius on some models. So I understand what you mean.good luck I’ll keep watching.

 

This is how I'm currently trying to do this, the rectangle is 120" long by 39" wide which represents half of the bottom, the bow intersection is 8" inches from the bottom and the tangent point is 120" , large inside circle is 1589 " and the small outside circle is 509", roughly a 3 to 1 ratio.

 

I thought you might be envisaging a jet boat. And I also thought you were intending to build in aluminium. Wrong on both seemingly. If your are building in ply, and are worried about the maximum bending radius you can get away with, for a certain thickness, there are tables available that you can consult. But it would be a lot easier to just buy some plans for a boat that you like the look of. This is a fairly standard kind of planing hull you are talking of, and there is no need to re-invent the wheel. At the least you need a plan of the three-dimensional shape, and also an understanding that the lines are developable, that is, will be able to be sheeted so that it conforms to the plans. You can't get a sheet of paper to conform to the surface of a bowling ball, without wrinkles, which is an extreme example. but you want your sheets to fit your framing snugly. Which is not overly difficult, but needs an understanding of the shaping limitations.

 

I am building it out of Aluminum, the wood is just for a pattern mock up to see what might be possible, since I have a cnc and 1/4 ply is much less expensive the 5086 I have no problem tossing out a few sheets. I know that aluminum will act different then ply when formed but I think I can get it close enough that I will never know the difference. I have a friend who does 3d modeling with rhino and I'm going to hire him to make some basic plans so they can be cut out of the cnc. I also have fusion 360 that I have been working with. Thanks for your reply!

 

The problem of sheeting hulls in a way that the material takes up the curves easily, is achieved by making the surfaces developable, much like what sheet metal workers work to. Without precise drawings, that is difficult, especially if you want to fabricate in a way that the frames are everywhere in contact with the sheeting.

 

There's not going to be any frames, that's the beauty of these boats the bottoms are made out or 3/16 or 1/4 inch the sides are made from 1/8 after the boat is formed the front end uses a spreader bar to hold its shape until the storage, rod lockers and fish boxes are welded in. the bottom has 4 stiffeners welded the length to where the bow curve starts ( bulkhead) then some channels welded from there up the radius of the bow. it has some cross members to support the floor and thats about it.

 

If it’s going to be constructed similar to the boats in your photos, they have frames in the curved sections. That’s what those plates are. Are you going to be assembling it significantly differently than them? The straight runs are easy - do what you want there.

Who’s the builder in those pics? In Oregon?