This seems like a thread that might be able to answer a related question that has been nagging at me for a while. I am mostly concerned with how shallow the water can be for practical sailing (this would be, for example, cruising off the south tip of florida, inside the florida keys).
Each of the harryproa configurations I have come up with ends up with a very shallow draft on the leeward hull (usually 6-9" when sailiing flat). My impression is that you will probably want to allow at least 18" of rudder in the water for steering. So, it would seem like I could put a stub keel on the bottom of the leeward hull which is about 12" high and maybe 10' long to help with leeway prevention.
My question is, what does the additional wetted surface area do to the overall performance of the boat? To put some numbers on it for my wooden boat competition entry, the wetted surface area for my boat are:
lw hull: 80 sq ft (1.5' hull beam with semicircular underwater profile)
ww hull: 70 sq ft (2' hull beam with 1' flat bottom and 6" radius curved edge, with a 1' draft)
if I added a 1' stub keel, 10' long to the lw hull, that would add 20 sq ft of wetted surface, an increase of 13%.
So, does this mean I would lose 1 kt of boat speed at 12 kts (i.e. would I go 13 kts without the keel)?
Also, what effect would this have on leeway prevention?
- Gardner
Rudolf
There is performance merit in resisting leeway with a non-ventillating foil or foils. Once this is achieved it does not matter much how the boat is steered unless the rig is poorly balanced. I am now thinking dipping rudders a little more sophisticated than what Tarawa is using would be my starting point.The other conclusion is that a slab sided or very deep V (> 45 degrees) hull will be as effective at resisting leeway as ventilating rudders. So a reasonably elegant solution is exactly what Tarawa has in concept. It could be engineered with a bit more precision.RickOn 16/05/2011, at 11:16 PM, Rudolf vd Brug wrote:
Arto,That's exactly what I was wondering:to keep thing as simple as possible could a keel with two small retractable rudders work well?And I mean a keel put onto the same hull you would use having boards, not a deep hull like Tarawa as that would have more wetted area.Can you say anything about that Rick?Rudolf----- Original Message -----From: Arto HakkarainenSent: Monday, May 16, 2011 2:04 PMSubject: Re: [harryproa] Re: Design your proa