Design project

Hello,

I'm attempting a design project as an absolute beginner. I've read several books on the subject, and hae set myself a goal of designing a boat from scratch to continue to learn.

The boat is:

Weekend coastal, harbour and river cruising to sleep 2 cofortably, 4 with a squeeze
9 m LOA
3 m max beam
Hard chined
plywood /epoxy sandwich construction

Here are a few pictures of the preliminary hull lines from freeship - I would love some feedback on the general hull form.

Many thanks in advance.

 

one more ...

 

First glance looks good, but can you give us a few more details, especially the speed you would like to do and the power, etc. Do you have the displacement and any other parameters?

 

Thanks Crag,

Freeship tells me the displacement is 5.606 t, however, this is very preliminary, and I'm yet to actually work out how much displacement I need, and exactly where the DWL will be. I'm working through the scantlings now to try and work this out.

I'm planning for this boat to operate at displacement speed, so I think that is about 7 - 8 knots. I plan for it to be an efficient and comfortable cruiser that slips through the seas.

Prismatic coefficient is .59 - which I think is a bit high for optimum, but I would be interestd to hear your opinion on this. Longtitudinal centre of bouyancy is at 4580mm.

I haven't worked out the displacement/length ratio yet, or done any calculations on power requirements.

 

I dont think Cp=0.59 is to high for the speed you plan.
See for example http://www.tedbrewer.com/yachtdesign.html
If your boat is 25 feet on the waterline,7 knots is a Speed/Lengt = 1.4, so CP=0.64 should be OK.
If you cruise at 6.5 knots S/L=1.3 -> Cp=0.62.

I don't know your Lwl, so 25 feet was just to make calculations easy
The boat looks good.

 

Thanks for the feedback - that all makes perfect sense.

One other question I have about this hull is the stern. I notice the stern on many displacement hulls sweeps up gently out of the water. Are there any adverse effects (in terms of drag) from having the stern fully immersed?

 

At low speed you drag the water with you if the stern is submerged.
If you want to go faster than 8 knots (with your length) you may want to have a quite flat bottom in the aft sections and a submerged stern.