Design project

[Brands01]

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.

[Brands01]

one more ...

[Crag Cay]

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?

[Brands01]

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.

[Raggi_Thor]

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.

[Brands01]

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?

[Raggi_Thor]

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.