Sailing upwind - 1 board or 2?

[valhalla360]

Originally Posted by arsenelupiga

I doubt all the way down in storm. One needs to consider possibility of breaking board, which will cause some dramas for sure.

I still have copy of catana manual here that explains that clearly.

I don't recall saying it was catana specific advice but if you have deep boards with a significant potential to break, probably a good idea to limit how deep they go.

[mikereed100]

Originally Posted by UNCIVILIZED

If you're at all concerned about safety, sail with only the weather board down. That way, if you get overpowered enough, before you can ease a sheet. Then said board will lift free from the water (along with that hull). And in theory, you'll slide off to leeward, sans going inverted.
As there wont be a board in the water in that hull, restraining your transverse movement.

This technique is often stated and it is similarly touted as a safety advantage of having dagger-boards. It does make common sense but I think it is of questionable value in practice. For the most part one only uses the boards when going to windward. If it is windy enough to worry about being blow over by a gust the boards are already raised quite a bit if not entirely. The lateral resistance of the boards as a percentage of total hull resistance at this point is going to be pretty minimal. In the case of a wave strike the boards will likely be in turbulent water and the wave will furthermore have passed under the leeward hull before the windward hull can lift very far.

For the most part we sail with the boards at equal depth, whether raised or lowered as needed. The only time we have them fully extended is when sailing on a close reach in light air. Once the wind picks up and we are moving well we release the boards and let them float at about half-depth which, to be honest, is where they stay most of the time. We lift them completely if we are running or we want to increase apparent wind on a broad reach in light air.

[Nicholson58]

Originally Posted by Getweh

Yeah, Not much to be gained having the crew out on a trapese on a 45.

Funny,

[cwyckham]

I think it's understood by most but hasn't been stated explicitly in the thread yet that the lift to drag ratio of a wing is strongly influenced by the aspect ratio (length to chord ratio).

So you'll have better lift to drag from one full board than two half boards. This is why people are saying they tack the boards when racing, but just leave both half down when cruising and the better AWA isn't worth the effort.

[Metalcat]

Originally Posted by cwyckham

I think it's understood by most but hasn't been stated explicitly in the thread yet that the lift to drag ratio of a wing is strongly influenced by the aspect ratio (length to chord ratio).

So you'll have better lift to drag from one full board than two half boards. This is why people are saying they tack the boards when racing, but just leave both half down when cruising and the better AWA isn't worth the effort.

But what about 2 full boards vs. one full board?

[mikereed100]

Originally Posted by Metalcat

But what about 2 full boards vs. one full board?

We do a little better with both boards fully extended. Maybe racers have found that the increased drag is not worth the increase in lift? For cruising I feel it is beneficial to split the loads between 2 boards rather that place all the loads on one. Building boards is time consuming and I don't want to be sourcing marine ply and epoxy in the boonies.

Interestingly, tank tests have shown that one large board is more efficient than 2 smaller ones and several designers have gone this route.

[paxfish]

Originally Posted by Metalcat

But what about 2 full boards vs. one full board?

Speed is an important consideration there. 2 boards fully down generates a lot more drag of course. I use two at low speeds. But when hard on the wind, a fast cat is capable of 10 or more knots boat speed, and one board seems to be very capable on mine.

Someday I'll invest in fancy instruments to provide some comparative data on VMG, but for now I have to go on gut!

[44'cruisingcat]

Originally Posted by mikereed100

Interestingly, tank tests have shown that one large board is more efficient than 2 smaller ones and several designers have gone this route.

True. Unless you routinely fly a hull!

(We don't.)

[out42]

FWIW after trying all modes - one up, one down, two, etc etc, on two separate Outremers (with running backstays!) it appears that beating hard to get to a racing mark you get a better tacking angle with the two down fully. You might therefore make the mark you would otherwise miss.
If doing a long beat to windward then I suspect we go a little faster with one board down and can usually make up the lost tacking angle so better VMG overall.
Over about 10 knots hard to windward for us there is still some gain from having some board down as the leeway definitely increases when you pull it/them up. As soon as you are slightly off the wind, heave them up.

The only way really is to do the VMG work while sailing your own boat. Then you'll realise that better sails make more difference, etc, etc....

[valhalla360]

I think most people suggesting 2 boards part way down are cruising and just want to set it and forget it when out for a day sail.

Of course, I remember the first time we took ours out for a sail. We bought it in the winter and didn't get a test sail so our first time was by ourselves and our sailing experience was a 3 day class on a fixed keel mono. It was on one of the small lakes off Lake Michigan on a mild day (maybe 10kts wind and negligible waves), so no worries. We were having a nice time and figuring things out but looking at the GPS plot after the 3rd tack that showed us just going back and forth on the same line. I realized, we had no boards down. Popped below and put a board down and suddenly, we made much better VMG to windward.