I posted this question a few years ago and couldn’t get an answer, maybe this time. I have built 4 Mistrals with varying deck designs but with the fin and rudder according to the plans. All of them sail nicely but I have to have the mast at least 2 1/2 maybe 3" forward of the front of the keel to have them balance out with just a touch of weather helm. Can anyone give me an idea why??? The plans say about an inch. The boats float on the waterline. I use the US1M “A” rig. I make my own sails. Any ideas at all?
Thanks
Don
Do you make your sails with a large roach curve? For some reason the center of effort of the sail has moved aft, causing the mast to be moved forward for balance. Calculate the COE and COLR out and see.
http://www.wb-sails.fi/news/SailPowerCalc/SailPowerCalc.htm
http://www.seadercraft.com/sail_crafting.html
Mitch
The sail plan is a standard US1M “A” rig. The boat would have been designed around this sail. I have tried a set of Gordon Stout sails with the same result.
Don
Well, it’s gotta be the sails or the foils.
Is the keel foil in the correct location and is it on the correct swept angle?
Is the rudder the correct size and at the correct location?
If these are correct then it’s back to the sails. Is the mast raked aft? It could be sail trim but I doubt it would cause that much mast movement.
I guess it’s possible the mast location on plans is wrong, which would return me back to calculating the COE and COLR and see how they line up.
MItch
I calculated the COE and COLR and the COE is approx. 6" forward of the COLR. That is within the 10 to 20%. The Mistral is also used as the ODOM. I asked those guys if they had bad weather helm and they said no. Today being a quiet day I was surfing a lot and found the ODOM site with its sail plan. It is quite different than the US1M “A” rig. US1M main is 304 sq. in.,ODOM main is 293. US1M jib is 289 and ODOM is 312. It looks to me that the Mistral with the “A” had weather helm issues so when they used it for ODOM they changed the sail plan to compensate. Sound logical?
Don
That would move center of effort forward and would help the balance problem.
6" is alot for a 1 meter boat, I’m suprised that is what the plans called for. You might try posting the same question on http://www.boatdesign.net/forums/
Lots of knowledgable Naval Architects (and want to be’s like me) that might have some more insight.
Best, Mitch
I think I may have discovered what was wrong. I was looking at the other free US1M plans on the AMYA site and noticed that each plan had an associated sail plan and they were all different. I was under the assumption that all the boat plans were drawn to work with the standard “A” rig. When I built my first boat(a Mistral) I downloaded the construction files and assumed that the sail plan in them was for the Mistral. I now think that when the Mistral was designed it was designed to work with the sail plan that the ODOM uses which as I mentioned about two posts up has a larger jib and smaller main. Therefore I think I have been using the wrong sails and now that I look at it it does say that the “A” rig is for 5 mph or less. Now all I have to do is figure out how much main area to move into the jib still keeping the same high aspect ratio.(I think it looks cool).
Just in case anyone is interested
Don
Hi Don -
your question prompted me to take a look and measure a Victor “IL MORO” boat that I have waiting to be worked on. The hull is supposed to be a derivative of the MISTRAL, but I can’t tell where/what is different.
For what it’s worth, the mast location is approximately 16 1/2 inches aft the bow - and the leading edge of the keel is approximately 1 inch further aft ( at 17 1/2 inches)
These measurements are parallel to deck - but since the boat remains unbuilt, it is best guesstimate of where they are located. Also - the sails on the IL MORO have a jib that is at most 3/4 size… as compared to the jib associated with the ODOM.
Not sure if this helps, but at least you have a few measurements to use to check yours - but no way I could move the mast another 2 - 2 1/2 inches forward. Good luck with the fix.
Dick
Could you post the measurements of the sail, please? I would imagine that they have the 1.5 and 2.5 roaches? The Mistral plans call for the mast to be approx. 19.25" from the bow and the front of the keel is about 1" behind that. I sail with the mast about 16.5" back. Thats strange that the Il Moro has such similar lines but the parts are in different spots.
Don
Don -
Dimensions shown are for jib and main - first is luff length, others are chord lengths at 1/4 intervals with first being the headboard size. Taken from class sail control drawings - all are in inches and are from top to foot of sail.
JIB
Luff 45.75
Headboard .5
4.5
7.5
10
11.5
MAIN
Luff 52.5
Headboard .75
6.375
9.5
11.375
12.5
Hope this helps - Dick
Maybe take some cheap ripstop nylon and make up a set of single panel sails to these dimensions and see how it sails. You can always cut down the nylon after to make a storm set.
I’ve got a whole bunch of 3 0r 4 mil drafting mylar that I liberated from work when I retired. I looked at some pictures of Il Moro and that swept back fin effectively moves the fin back an inch or so. Thanks for the measurements.
Don
No problem - let me know how I can help.