Getting out on the water this year

What does your design brief look like? What are your requirements for the boat? What do you want to use it for? What does your budget look like?
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Manik
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Posts: 373
Joined: 27 Aug 2014, 15:41

Re: Getting out on the water this year

Post by Manik » 16 Apr 2015, 09:37

Hey guys,

I've been really strapped for time lately, and will be for another two and a half weeks or so, so just a very quick update. About a week ago I had a look at some of the numbers (WSA, B/L, DLR, and moment to pitch 1° amongst them) for four different configurations.

What I found in particular was that the overhanging bows and increased flare which the Wharram-inspired design brings with it, increases the DLR and decrease the L/B ratio and the moments to pitch 1°/5° significantly, while the decrease in WSA is minor. This has me going back to something much closer to the original, but with increased beam, increased freeboad, and very slightly increased flare to make the interior more roomy.

The difference in moment to pitch 1° was what really caught my eye, for the same bow half-angle, the hull with the vertical bow and less flare has so much extra volume in the forebody that the moment to pitch 1° was 2000Nm as opposed to the Wharram-inspired hull's 1650Nm, that's a whooping ~20% extra. Since form stability will probably play a large part in the overal longitudinal stability, I think the difference in overall sail carrying ability when beam/broad reaching, and the difference in damping pitching / hobby-horsing could be quite significant. Improvements in DLR and L/B were also on the order of 20%, with a mere 1.5% penalty in wetted surface area. The bottom line is that the old hull, but modified to be a bit more roomy, would probably have very noticeably improved performance over the Wharram-inspuired hull, so that's the road I'm going to take. Aestehtically, I like the Wharrams' coachroof look, so I may well opt to retain that feature.

From a construction standpoint, I think it's wise to have just enough flare at the vaka midsection to allow stepping the mast to windward of my planned pilot house, without having to construct a windward step / minipod of some sort. That cuts down on what I think would be a lot of unnecessary hassle in the build. The issue of a lee pod vs. a safety ama remains, though my tendency is toward a lee pod (without a bunk), even if the resulting angles of heel in a knockdown are far higher than I would like. The tricky part is working out some way to make this work where the hatch / companionway is concerned, but more on that in a few weeks. ;)

Cheers,
Marco
"Man's mind and spirit grow with the space in which they are allowed to operate." - Krafft A. Ehricke, rocket pioneer
RobinBennett
Posts: 129
Joined: 08 Feb 2015, 22:36

Re: Getting out on the water this year

Post by RobinBennett » 17 Apr 2015, 22:00

I was thinking about the problem of spray going down the hatch/companion way, and wondered if anyone had tried a standard hatch and windward cockpit (like Madness, etc) with a spray dodger around the windward edge? You could leave it down if you're worried about the windage and fold it up when you want to open the hatch, or just want more protection from spray and rain.
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