-Hi George.
I agree that bows digging in are a significant part of pitchpoling, but merely having the bows go under is not necessarily going to cause them to dig in. provided the bow is not severely depressed(too little bouyancy) the transoms are not in the air (too much rocker0, have a sudden increase in resistance (flared bows) The way I understand pitchpoling is when the resistance of the bows suddenly increases and there is either too much sail up , especially and/or the cog is too high and the momentum contributes. The way I understand it is the lower the bouyancy of the bows the better to prevent pitchpoling as it keeps the transoms down- especially with no rocker. As the load comes on, if the bow gets narrower, the wave resistance decreases, reducing the chance of a sudden increase in bow resistance. Any bouyancy above enough to lift the transoms out of the water when fully loaded is too much and increases bow resistance. Underwater a bow can be rounder for minimal resistance At the waterline it needs to be sharper or reversed. With reverse stems it is easier to make them somewhere between a teardrop and an egg shape. As the bows depress, the narrower bows at the top reduce the impact of the waves and also wave induced drag. Also, for getting through waves, a reverse stem that is fatter on the bottom damps pitching. Going to a knife edge at the top starts to increase induced drag from winds across the bow so a bit of rounding needed. In profile I have drawn the bows of the Harry I want looking like an albatross beak. There is a concern about going too flat on the bottom of the bows in the event of coming of a wave and slamming down, so I would put a shallow V for the first metre or so
Back from the bows a rectangular box with rounded corners makes sense to me as it is easy to make with least 'not on the table' glassing and is a suitable shape for going to a schooner rig. This should be enough to keep bouyancy high in case of a knock down, especially as this area is about 8-900mm higher than the bow. I have drawn a 40cm flare on the inside of the lw bow from between the cross beams then tapering to the top of the bow about a metre back from the top of the stem. The idea here is to start lifting the boat before the crossbeams hit white water. It also provides a place to hang the rudders and leave the crossbeams clean for telescoping.
For the windward bow, it is very different as the hull lifts as the bow depresses. For the ww bow I have been drawing up designs with a bow bulb to reduce impact of chop. The bow then going to a slight reverse stem with spray rails to keep the boat a bit drier and possibly give a little lift. The spray rails widening out into a 250-300mm flare a couple of metres back to increase the accommodation- similar to a small tri. In profile the ww bow looks similar to a Cape Barron goose head
The bow bulbs also becomes a step to get on board from the water or beach.
A disadvantage of a shunter is that you have to have both ends acting like both transom and bows. I feel that theses designs acommodate this. An advantage of a shunter is that for multihulls the lee and ww bows act very differently and this can be accommodated.
In the event of a knockdown, I have been thinking of Rob's idea of having the bearings off set so when the wind is on the beam the mast is raked forwards, and when hard on the wind the mast heals to ww. If the boom is fixed to the mast, you have a balance between the boom in the water and the mast in the water.
In harryproa@yahoogrou
>
> Hello Rober,
> I would not go too skinnier, It is a combination of boyancy and rounded shape to prevent bows diggigging in or pitchpoling.
>
> Happy sailing,
> George Kuck
> Chestertown, Md.
>
> --- On Thu, 6/11/09, Robert <cateran1949@
>
>
> From: Robert <cateran1949@
> Subject: [harryproa] Re: preglassed panels....weights.
> To: harryproa@yahoogrou
> Date: Thursday, June 11, 2009, 9:32 AM
>
>
>
>
>
>
>
>
> -DOn't understand DER.
> I agree about wanting rounder foredecks on the lw hull. It would shed water much better. I'd go further and have the top of the bows much skinnier than the bottoms. -- In harryproa@yahoogrou ps.com.au, Doug Haines <doha720@ > wrote:
> >
> >
>
>
>
> Recent Activity
>
>
> 41
> New PhotosVisit Your Group
>
>
>
>
> Y!7 Toolbar
> Get it Free!
> easy 1-click access
> to your groups.
>
> Yahoo!7 Groups
> Start a group
> in 3 easy steps.
> Connect with others.
> .
>
Change settings via the Web (Yahoo! ID required)
Change settings via email: Switch delivery to Daily Digest | Switch format to Traditional
Visit Your Group | Yahoo! Groups Terms of Use | Unsubscribe