Fairing in bulb to foil

[jray]

Did most everyone glass the bulb after attaching the strut and fairing? That was my thought but wanted to ask the advice on which direction most went with. Thanks!

[Ron Bowman]

Hi Jon,

I did not glass my bulb. Just faired and painted it.

Ron

[jerome]

İ still do intend to glass mine but just for abrasion purposes. Before this thread started, my game plan was to heavily laminate the bulb to foil. Now that İ have learned all about it, İ will just use a minimum of epoxi-colloidal and NO fiber to leave that area as flat and squared as possible. Just like the big guys ! But İ will nicely fair and glass the bulb itself.

[Kevin]

I just bolted mine together and to the keel fin. Then I filled and faired it together. No time spent glassing the lead bulb. If it get's scrapped up, then it will get refinished (some day) was my feeling. If you make it bigger, you are just creating more drag too.

Kevin.

[jeff.dalsin]

Jerome-

I don't think you will get the abrasion resistance you want by glassing the bulb. I thought is that bulb has such concentrated mass, and therefore high inertia, that substantial contact with anything will pierce the glass skin becuase the underlying lead is quite soft. My 2 cents.

Jeff

[jray]

Not taking the extra time to glass the bulb will be great. Still have a lot of fairing to do to get everything right. Thanks for the input everyone! All goes well it should be well underway before the weekend is over.

Edit . I'm going to cross bolt to the strut, any thoughts on bolt size? I will probably use standard zinc coated bolts. My thought is two 1/2" bolts.

[Kevin]

I used 1/2" bolts. 2 in the bulb only (way forward and aft) and then 2 through the keel strut (fin). After drilling the holes, I'm pretty sure the bulb only bolts were not really needed. Ron just did the bulb to fin bolts.

k.

[slowpoke]

I did three bolts, one 1/2 inch at the thickest point, and two 3/8 inch further aft. Actually used all-thread, so I could cut them to length as needed.

[jray]

That actually sounds good Rocky, I might be off but in regards to the bolts attaching the strut, the bolts are under a sheer stress not a pulling or stretching. Thanks for adding to the options. I'll probably over build as is normal for my thought process.

[slowpoke]

Don't forget to drill the holes in the foil oversize, then fill with epoxy, then re-drill to the correct size. I don't know for sure if you really need to, but i figured better to be safe...

[Kevin]

yes yes and yes. Always drill and over sized hole, fill and then re-drill the correct sized hole. Water will find a way in eventually. It is the enemy and it will win given enough time. Threaded rod with nuts on both ends isn't a bad idea either. Usually the nuts are smaller than the bolt heads which will allow slightly smaller holes for them.
Cheers, k.

[jray]

Here is another question. I shouldn't be allowed to over think things, it only slows the building down.

Has anyone considered the different rates of thermal movement between the lead bulb and wood keel strut? I deal with this often between wood and metal at work. My thought is to get the bulb filled in around the strut leaving about a 1/6" around and using a product like G-Flex for final assembly. My concern is with using a ridged epoxy that might develop cracks as time goes by, having the boat in and out of the water. Any thoughts?

[Chad]

Wood does almost all of its swelling and shrinking with changes in moisture content. Thoroughly seal the wood with multiple epoxy coats (unsheathed ends, especially), and it becomes very stable. The lead is likely to have a larger thermal expansion rate than the foil, so GFlex isn't a bad choice to cope with any minor movement. GFlex still dries "hard", just not brittle-hard like typical non-toughened epoxy. It shouldn't be thought of as a caulking substitute that is able to handle gross movement, for instance.

[Kevin]

g-flex has a 30% elastisticity compared to regular epoxy that has about 2%. So if you are using some of that g-flex 655 that you got to put your mast together, then I'd agree with chad that it sounds like a good idea. I had pretty uneven gaps around my keel so I used silica filled epoxy. I didn't notice any issues after my first year of sailing, but we are still early in the life of the boat.
k.

[Chad]

RM90 keel test:

IMG_0603.JPG

Hmm, should I start on MKII now, or just wait for this one to become fish habitat first?

[micah202]

RM90 keel test:

IMG_0603.JPG

Hmm, should I start on MKII now, or just wait for this one to become fish habitat first?

...hmm,maybe jump up and down on the bulb to replicate slamming in waves

,,,,,,, ,,maybe not

[Chad]

[rationalizing] let's see, sin30 is half of sin90, so as long as I keep the heel angle under 30 degrees, I've at least got a safety factor of two. Hopefully, no slamming occurs when the keel is at 90, though! ...or nobody bails over the high side to stand on the keel...
[/rationalizing]

I think it'll do for my local lake, with flat water and generally light air. Winter's coming, and I'm sure I can use an extra project or two.