Gardner,
We come back to the moment of inertia issue. Which place on a boat is located longest distance away from the center of gravity? Mast head of course. All the weight there has the longest lever arm there is when the boat is pitching or rolling and that lever arm is quite long. So in addition to reducing the stability it also has all the negative effects of weight at the ends multiplied by the longest lever arm there is on the boat. So the winglet may improve aerodynamic efficiency but be very careful about adding the weight. Monohull racers talk about removing grams from the mast head, some are even ready to remove the halyard blocks and leave just the axle of the block to the mast head to reduce weight...
Arto
--- On Wed, 6/8/11, Gardner Pomper <gardner@networknow.org> wrote:
From: Gardner Pomper <gardner@networknow.org>
Subject: Re: [harryproa] Span Efficiency - Another Harryproa Opportunity
To: harryproa@yahoogroups.com.au
Date: Wednesday, June 8, 2011, 2:03 AM
Rob,
Yes, the discussions of upper winglets on monohull forums always hit the "weight in the wrong place" argument and quit. I can see that argument for multihulls, because of rolling, capsize, etc. I can even see it for racing multihulls, which may want to sail heeled over to fly a hull. I don't see the relevance for a cruising multihull that is never intended to fly a hull. If the hull ever lifts, even a little, you will do all you can to depower as quickly as possible, so your heel angle should not even exceed 10 degrees. (ToyyoT is heeled about 3 degrees when the ww hull flies).
So, it would seem that an extra 10 lbs at the top of a short mast should not make a significant difference. Am I just naive?
- Gardner
On Tue, Jun 7, 2011 at 6:16 PM, Rob Denney <harryproa@gmail.com> wrote:
Steve Dashew tried tarps under the boom on his 65' mono. Reckoned they made a huge difference. Loic Peyron tried a wing tip at the top of an ORMA 60 tri mainsail, took them off soon after. Top ones are a problem as they are weight in the wrong place and because they contribute to capsize when seriously heeled. I have some ideas for a masthead tip which stays horizontal which I intend to try on El when the new mast is built.
rob
On Wed, Jun 8, 2011 at 3:59 AM, Gardner Pomper <gardner@networknow.org> wrote:
Rick,
I have been trying to poke around to see if anyone has ever tried putting endplates on sails; both the foot and the head and I find a bunch of discussion, but no trials, even theoretical ones. From your explanation of how much using the deck as an endplate helps when close to the wind, it made me wonder if it wouldn't help on most all points of sail, once you are dealing with a rotating mast. Won't you always have the sail trimmed for close reaching, and it would then also benefit from the endplating even on a beam reach. Does it actually matter which way the hull is pointed, or is it just effected by sail trim?
The only actual trials I have seen are on the wing tips of RC planes, where just a square tip made a big difference. Wouldn't it be possible to just attach a 2'x6' piece of laminated foam to the top of the sail? That would only weigh about 5 lbs.
So, I guess the questions are: how big does a boom or head plate need to be to get the span efficiencies up, and how much drag would they add? (assume for arguments sake that we use 9mm foam glass on both sizes, so 8oz/sq ft at most for weight).
- Gardner
Arto
Anything that creates flow resistance from the pressure side to the low pressure side helps with span efficiency. Adding bits to achieve it gives diminishing return because the added bit adds drag. The deck of the lw hull is there anyhow. Bringing the boom down to the hull does not add more drag area.
Rick
On 06/06/2011, at 11:52 PM, Arto Hakkarainen wrote:
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I suppose that a really wide boom such as "park avenue boom" is not sufficient to end plate the main? Or is it?
From: Rick Willoughby <rickwill@bigpond.net.au>
Subject: [harryproa] Span Efficiency - Another Harryproa Opportunity
To: harryproa@yahoogroups.com.au
Date: Sunday, June 5, 2011, 5:50 AM
Looking at the mast and boom on Peter's boat yesterday the topic of span efficiency came up.
Also when I was working on the parameters for Gardners schooner rig to plug into the VPP I had to take at stab at the span efficiiency of his proposed sail plan.
This is something that I have discussed with respect to rudders and daggers but I don't think it has been discussed with sails. Although I have referred to aspect ratio rather than span efficiency. In effect the induced drag is halved if the blade is effectively end plated against the hull or if a surface piecing blade is at high speed and non-ventilating. End plating is equivalent to doubling the aspect ratio or span efficiency is 2.
Anyone who has sailed on a sloop rigged keel boat knows how the pointing ability improves when the genoa is sheeted down against the deck. This increases the span efficiency of the rig. There is little or no air spilling under the sail.
Another good example is Macquarie innovation. They went for a low aspect wing but were able to improve the span efficiency by setting it close to the water:
Wing end plating is something I proposed for my beach proa. It can also be achieved with the schooner rig Gardner is proposing.
The sail efficiency is most important when sailing close to the wind and in these angles just the lw hull provides reasonable end plating.
Gardner - For the VPP I produced I selected a span efficiency of 1.3 based on what I have read about bi-planes. If you "end plate" at the bottom the span efficiency lifts to 2.
There is some work being done with winggrid winglets that get span efficiencies above 2:
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