Boat design help

Hi I have been working on this boat design: Onshape https://cad.onshape.com/documents/134d28341a5a6d2f65af1ace/w/85d5090e44735e8b83e198ec/e/52e03770709269cbb34c8973

Any advice on things I should change I would appreciate it. I have no prior experience to designing boats.

Thanks for any help,
-Noah

 

Noah, give us more details. What size boat? What is its purpose? It appears to be a go fast dinghy with hiking wings.
Post some drawings of the plan view, profile view and section views of the boat. Only then can we offer pertinent advice.

 

Length: 11 ft
Beam: 3 ft
And yes, it is a racing dingy

 

It looks like there is a bit of Moth influence there - have you previously sailed Moths?
British Moth - Wikipedia https://en.wikipedia.org/wiki/British_Moth

Are you planning on building your design?
Are you thinking about adding foils as well, as per the more recent (and very radical) Moths?

 

You have shown a much rounded section view. Too much curvature if you hope to have the boat plane early. The boat will be very tender with this section configuration. almost unmanagably so with that sail and mast up there. Flatten the below water sections to gain some initial stability, all though the narrow hull will always be a bit tiddly. The shape of the fore and aft keel line could use a bit of adjustment if you want the boat to plane more easily. Move the lowest part of the keel forward to a little less than 50% of the length if measuring from the bow aft.. You are trying to make the run of the bottom as straight as you can with the smallest run angle with respect to the base line. there are compromises here because you need to get the transom a little bit above the water line. To do that carefully you have to do some buoyancy calculations for the entire boat while making a reasonably calculated estimate of the overall weight of the boat, rig, skipper, and whatever else is in or on the boat.

There is no need to angle the transom unless you plan to use an outboard motor on the boat.

Keep working on this you may even come up with a competitive design. If not, it is still fun to try. Paper and pencil is cheap. A lot of drawing options are worth working on.

 

For a first design it looks interesting and quite complete.I hope you will take my word,as a former Moth sailor,that you can expect anybody who steps aboard such a craft to do a lot of swimming.If you have done any amount of reading about boat design you are likely to have come across references to the "design spiral" and you will be taking a trip through it as you deal with some of the details.One of the most important phases is dealing with the weight and thus determining the waterline location.How much work have you done in this direction?Another element that needs some work is the matter of actually steering the boat;the sloping transom looks quite fast (even if it doesn't actually affect the performance) but doesn't make it particularly easy to find suitable hardware.I suggest you seek out an available rudder stock and work out a way to attach it to the hull.It would help with the ergonomics if you were to add a mainsheet and a tiller and checked whether the average size sailor can actually find a gap to pass through when tacking or gybing.

A couple of other points;how much sail area have you selected?How high will the boat float when capsized-which it will be likely to do fairly often-as the occupant will have to get to the daggerboard to begin the righting process.Good luck with the process as it can be a fascinating interest and it will take you to all sorts of interesting places.

 

I have not sailed on moths but have sailed next to a waszp
I hope to build to build it, but most likely not for a wile.
I would love to add foils but they seem to hard for a first boat project.

 

What you're saying makes sense, I'll revise the design. Should I use graph paper to model?

Thanks for your help I'll post my revised design when I finish

-Noah

 

For reference that might help with keel rocker you can do much worse than seeking out pictures or lines plans of Low Rider Moths.They might also help with section shape.Having never used Onshape I have no idea if it has any way of calculating underwater volume.If you can create a solid and then split it with a plane surface,you might be able to determine the volume and hence displacement that results.It can be done with graph paper and often was but it is a lot more work than clicking a mouse a few times.

From a practical point of view,how are you proposing to hold the mast up?The hull is quite fine in the bow and doesn't permit a wide spread to the shrouds (if any are planned) while an unstayed mast will impose considerable torsional loads.

 

What do you think of this: Onshape https://cad.onshape.com/documents/765b36c5febd3d48cea91094/w/2f9fb3d1b4304f4bebf90437/e/d6f89d4e4eea30b499cc13d7

Good point about the mast, what about connecting the stays to the hiking wings.

 

The waterline is at 5-6 inches up the side of the boat. Is this okay?

 

The location of the waterline is something you can only determine after arriving at a reliable estimate of the weight of the entire boat plus the sailor.The immersed volume has to displace this weight of water and differs lightly between fresh water and salt water as sea water is a bit denser.

The trend for Moth shrouds seems to be to attach them to the wings and to place a strut between the attachment points,as you will hopefully see here:

 

I calculated the water line with a 400lb total weight.

Yess i Can see thank you.

-Noah

 

Four hundred pounds, for a boat of that size, is more than usual, for sure more than is wanted. A hot rod boat and rig of that size ought not to weigh more than 100...120 pounds. A normal sized skipper...figure 175 pounds or less, and we have a displacement of 295. design for that number plus maybe ...6 or 8 percentage points. Anticipate that there will inevitably be some water on the deck or in the cockpit. Every little bit weighs something. Strive for the lightest possible all up weight consistent with having the boat stay in one piece during a brisk wind event.

If you are a really big guy of 200 pounds or more, make the boat longer and maybe a bit wider.