Well I got my new sail winch and remote for christmas (it’s nice to get what you ask for from Santa) and my wife got the Drill Press she had on her list ( i am sure thats what she put down LOL) so my next IOM is in full swing , I have 3 months till the lakes thaw here. What I was thinking of using for my fin is a old windsurfing pointer fin I have. It is made from G10 and looks like carbon as well, it is very stiff and maybe a little heavy. I down loaded the IOM weight budget guide and it says a fin should be 108grams mine is around 200grams but that is weighting with my cheep plastic kitchen scale. Would this work, I will most likely try it anyway as I can make a new fin if I need to?
Hi A.B.
I race IOMs out of Vanvouver Island.
Only you can answer your question about the fin. Here are some thoughts that may help you decide.
The main question is “Are you building a ‘pond yacht’ or a competitive IOM?” .
If you are building a boat for competition, then the fin must be removable so that the fin/bulb can be weighed. This means that you must build a fin box in the hull. If you use the G10 fin and later decide to build or use a ‘normal’ IOM fin then the dimensions of the fin box may be an issue.
If building for competition, then the weight of the fin is an issue. A heavy fin requirs that you remove lead from the bulb. This raises the CG of the fin/bulb which is bad. If you later decide to make a light fin, then you have to add weight back into the bulb.
I don’t know waht a G10 looks like, so I have no comments on the wetted surface, airfoil, or shape, but these are important issues for top performance.
If you are building a pond yacht, none of this matters.
Hi AB
Good windsurfer fins are usually well made and well shaped and very tempting to use on an IOM, but may have a couple of drawbacks if you want anything competitive. Most serious problem is they tend not to be deep enough after you’ve figured in the requirement for a tongue in the hull fin box, you’ll need something around 500mm to start with. Next problem is they tend to be rather thick, with t/c ratios around 10% or 12%, while modern RC fins are around 6% or 7% t/c for significantly lower drag on the run. Finally, G10 is a little heavier than c/f and your bulb will be correspondingly lighter giving you a CG higher than others… Good luck!
Thank you Hiljoball and lester, I plan on just pond sailing with my two IOM’s with my kids and anyone else that would like to try. I have made a fin box that is in the other boat that way I can switch fins between boats or easily make new fins. I measure the fin and at the widest part on the cord it is 80mm and the thickest part is 7mm. I might try to bring the weight down by drilling out the section above the hull in the box. It is very stiff. I found some other matterial on a commercial construction site used to make walls bullet proof , it is 6mm thick and looks like lots of fiberglass layers compressed together. Hilojoball just google G10 and you will see some good sites.
Hope this attachment works. I also plan on straighting the trailing edge more vertical.
http://www.rcsailing.net/forum1/attachment.php?attachmentid=1357&stc=1&d=1198781667
Quote “If building for competition, then the weight of the fin is an issue. A heavy fin requirs that you remove lead from the bulb. This raises the CG of the fin/bulb which is bad. If you later decide to make a light fin, then you have to add weight back into the bulb.”
So how much fin weight is to much? or is stiffer better?
New question is do you sail the boat over minimum weight to have max bulb fin weight or do you lighten up bulb and sail boat at the minimum weight? Would this mean you would have to go to B rig earlier?
The IOM has a min and max for the fin/bulb assembly. As you want the weight as low as possible then the ideal is a fin that has no weight so that the entire weight is in the bulb.
The ideal fin has near zero weight and is very stiff.
The IOM also requires a minimum overall weight for the complete fully rigged boat. So the ideal is that the bulb/fin is close to its max weight (for stiffness to resist heeling) and that hull be as light as possible. Finally add corrector weights in the hull as low as possible and at the centre of buoyancy to bring the boat up to minimum overall weight.