Doug
With regard to nose dive into the back of a wave.
In a single direction hull it is possible to reduce the tendency by having little to no reserve buoyancy in the stern and some rocker in the bow. Take a look at outrigger canoes and surfskis.
With a bidirectional hull if you put lots of reserve buoyancy in the ends you have more tendency to lift the stern and bury the bow. The worst circumstances is having a high stern that buries the high bow with large reserve volume that acts as a brake when you hit the back of the wave. This will cause pitchpole. You want a hull that is not much affected by the waves.
My take on it is that you want the dynamic lift at the bow to be positive when the bow is buried. The test is to hold the hull vertical above the water and drop it. If it goes straight down then that is not good. If it starts to rotate about the transverse axis to go deck up then that is good. Opposite is bad.
From my testing, flat bottom with some rocker in the bow is good. Flat deck is bad. The 90 degree "V" deck with a flat, rockered bottom so far seems to work very well. It does not need much reserve buoyancy. The amount of reserve buoyancy depends on the trim due to sail pitch moment, lift from wave pressure and dynamic lift. If you cannot get the bow up in the first place through weight distribution, rockered section and/or hull wave pressure then there will be no dynamic lift.
Rick
On 30/08/2010, at 12:18 PM, Doug Haines wrote:
From: Rob Denney <harryproa@gmail.com>
Subject: Re: [harryproa] mast bury - hull heights/freeboard
To: harryproa@yahoogroups.com.au
Date: Sunday, 29 August, 2010, 17:25
The less height and beam in the lee hull the better, within stuctural and accessibility limits. Sol2 is 400 wide, this is too much for a fat fellow like me to put bulkheads etc in and is too narrow for the beams. The next one is 600 wide across the deck. My deck thinking was the boat would be through the wave before the water needed to flow from the decks, so the extra windage of raising and rounding them was not worth the effort compared to the ease of building. The next one has a bit more shape in the hulls which enables more triangular sections at the bows, and possibly a reverse bow (see how the bending works out).No updates, Sol2 is in the yard while I wait for the 15m table (still!). El is painted (50 bucks worth of paving paint sprayed over 40 grit orbital finish and it looks fine. Low gloss (as required), raw carbon spots are mostly covered (should have sprayed a second coat on them) and it thins and cleans up with water. Should be tough and UV resistant. Waiting for the sail (slides replacing pocket luff and an extra 2m high) so I can beef up the mast at the slide locations, hope to be sailing this week.rob
On Sat, Aug 28, 2010 at 9:42 PM, Doug Haines <doha720@yahoo.co.uk> wrote:
Solitarry is a) very light for it's length and b) an experiment. I am hoping to lower the bows by up to 50% once I see how it works. The mast bury is irrelevant as it is supported by the beam at the top bearing, not the hull. If I toss the beam (pretty likely, but I want to try it first), there will need to be some extra structure added. The first harry had the structure in the middle and it worked well for the mast. The beams were on posts which did not work so well. Curved beams like the tris are a great idea, but a lot of work to build.
On Sat, Aug 28, 2010 at 4:19 PM, Doug Haines <doha720@yahoo.co.uk> wrote:
Hi,
I am uncomfortable with the very low height of Rob's solitarry, especially for the mast bury.
I was just looking at a C class video - their bows turn up at the ends to give much greater volume, while the rest of the hull stays quite low. I think this would be good on a lee hull of a harryproa.
Because there is so much material in the meiddle of the lee hull it would be nice to keep it down to a minimum.
Could you use some kind of extra bulkhead and maybe support struts to take the mast tube up higher out from the top of the hull? Also perhaps doing the same at the cross eam.
Those modern trimaran cross beams curve down sharply to the floats. I don't know what would be strongest. I would have tought that it would be OK to just make a small sectio of the hull come up to the extra height using extra material.
If you look at some of the pictures or calculate the surface areaas for buying the foam it is quite a lot goes into your lee hull on the old harry and visionarrys.
Solitarry is so much lower and smaller in surface area.
The ww hull must have height - to stand up in, though it could be kept pretty low down with a camping rapscallion style.
Doug
--- On Sat, 28/8/10, Rob Denney <harryproa@gmail.com> wrote:
From: Rob Denney <harryproa@gmail.com>
Subject: Re: [harryproa] Corrupt messages in group ???
To: harryproa@yahoogroups.com.au
Date: Saturday, 28 August, 2010, 7:24
Which message? Please send me (off list) the original and the date and time it was posted and I will have a look.rob
On Sat, Aug 28, 2010 at 4:41 AM, tsstproa <bitme1234@yahoo.com> wrote:
Whats with the corrupt and elongated messages. I responded to Doug's message(wings sail) post. Message seemed corrupted and lengthened. I'm no tech guy but something smells a little fishy!!! Sorry for not catching this sooner before I posted my respond.
Todd
Rick Willoughby
03 9796 2415
0419 104 821
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