Wednesday, April 18, 2012

Upward Force

I have a new question for all you Mothies out there. How much force does it take to hold the daggerboard down while sailing? I’d think that there must be quite a bit of force upward on the daggerboard while sailing between the weight of the boat crew and acceleration forces. The reason I’m asking this is because I need to re-design my daggerboard box to work with my ride height adjuster. The daggerboard box on Mothball 1 is a 1”x 8” rectangular reinforced box that has a tight insert that bolts into the daggerboard box at the top to kept the foil from raising above the deck level. Then I had a pin that mostly kept the daggerboard from falling out while sailing. However, I need to change some of these parts to make the ride-height adjuster work and that includes cutting off parts of the daggerboard box insert and many of the areas that bolt the insert to the boat. Clearly I need a major re-design here. So the questions remains, what’s the best way to hold the daggerboard down? The two best options I see are to simply beef up where the pin goes through the daggerboard and assume that it will hold up. But my other idea is a bit different and seems like it would be much stronger. The other ideas is to bolt a removable flare onto the daggerboard at the bottom of the hull, so instead of holding the daggerboard down from the top with a pin, the flare would push up on the bottom of the daggerboard box in an inset receiver and prevent the foil from moving, then I’d just pin it on the top again to keep it from falling out. I kind of like the flare idea because I could make the foil/hull interface much stronger and stiffer utilizing the beefy rectangular daggerboard box originally designed in the boat. How do other boats deal with this?

4 comments:

Desolate Mountain Man said...

Hey bob, I'm an avid sailor from the flathead and stumbled accross your blog, researching moths, and am going to be in helena for the next couple of months. I was wondering if i could swing by and check out your project. thanks for your time.

Eric said...

The Bladerider and others rely on the pin to keep the daggerboard from either raising or lowering. The load on the pin is reduced a bit from the tight fit at where the daggerboard (vertical foil) enters the bottom of the hull. I've noticed some play at the deck / daggerboard connection since the fit isn't as tight at this point. I've never looked closely at the Mach 2 daggerboard cassette so I'm not sure what improvements were made there. I would stay away from any flanges on the daggerboard itself. There are situations, ie crashes, where you would want to worry about the daggerboard falling out through the bottom and probably messing up your pushrods badly in the process.

Bob Abelin said...

Feel free, although MB1 isn't too impressive looking at the moment. Most of the parts disassembled for refinishing. Email me if you want to have a look.

b_abelin at yahoo.com

Bob Abelin said...

That's probably a good point. It is working after all, so maybe I shouldn't try and fix it. Yet...