I'm about to outfit my new Sith I was going to glass in the upper strap anchors, but it's a VERY light lay-up & I'm scared it won't take the stress There's extra Kevlar on the flats so I guess I'll just have to drill holes & mount the straps w/ bolts. I've never drilled into a composite anything & was wondering what to look out for. Should I center punch it? Start w/ a small hole? Put masking tape on prior to drilling? The lay-up is Kevlar/glass/Kevlar.
Thanks in advance.
Hmmm. My feeling is "don't drill holes in the boat". Even when using wide washers with wide rubber gaskets, they become stress points at the hole and can eventually result in fractures at the hole. Even on a thin layup, you can spread the anchors out a ways so they have more contact surface.
My $0.02 worth (and probably left you with change )
KNeal
C-boats Moderator
"Believe me, my young friend, there is nothing-absolutely nothing-half so much worth doing as simply messing about in boats."
There are issues about drilling into composites causing local delamination, but this is more important for aerospace parts than for whitewater boats.
The special bits sold for drilling aerospace composites look somewhat like the wood bits having a central sharp piercing portion and sharp, forward-reaching, outside flutes. I think that type of wood bit might cause less fuzzing or delamination.
One way to approach it would be to drill a very small hole at the target point, and then start the inside and outside holes by hand. The little central hole would locate the center point of the wood bit, and the pointed spurs would cut cleanly through the Kevlar.
Another consideration: Will washers and screws/nuts be enough, or do you need to glass on supplementary glass or Kevlar, especially inside?
For what it's worth I have had my Sith for 3 seasons now, asn as per Martin and Gwyn's recommendation I have drilled holes for strap nchors through the hull. No special precautions, just mark the position of the hole, predrilled with a 3/16 drill and then the final 5/16" hole.
Put some 5 min epoxy around the edge of the drilled hole to protect the fibers.
I used 5/16" bolts with large (2" diameter) stainless steel fender washers both in and outside to spread out the load, and sealed the lot off with a copious serving of Marine Goop.
Not a problem since, the boat is still as stron in the area se on the first day.
Cheers!
martin a.k.a. the great gonzo!
Everyone must believe in something. I believe I'll go canoeing - Henry David Thoreau
I don't understand why drilling a hole and bolting anchors to the hull or deck would place any LESS stress on the layup than the more standard method of attaching anchors with resin. If anything, when you resin the anchors to the composite layup you are adding some additional resin with fiber reinforcement, which should slightly stiffen the area. Also, the anchor will still have some ability to flex with the layup upon impact. When you drill holes you are removing material and increasing the possibility of delamination (frankly, I don't think that the washer and bolt adds structural strength to the layup; it just provides an obvious stress riser that won't flex with the layup when you hit something).
I would sand the attachment points throughly, fray about 1-1.5" of the ends of 1/4" or wider nylon rope, and resin them splayed out on the hull and/or deck with some West Systems Epoxy. If you want, you can also cover the frayed ends with one or more pieces of kevlar to provide further reinforcement and stiffness. As long as you first sand thoroughly, the attachment should be quite strong, particularly when you're working with a new boat. The only time that I've had an adhesion problem with this method was when I was attaching anchors to an older used boat and didn't sand as much as I should.
John Coraor wrote:I don't understand why drilling a hole and bolting anchors to the hull or deck would place any LESS stress on the layup than the more standard method of attaching anchors with resin. If anything, when you resin the anchors to the composite layup you are adding some additional resin with fiber reinforcement, which should slightly stiffen the area. Also, the anchor will still have some ability to flex with the layup upon impact. When you drill holes you are removing material and increasing the possibility of delamination (frankly, I don't think that the washer and bolt adds structural strength to the layup; it just provides an obvious stress riser that won't flex with the layup when you hit something).
Hey, I never said that drilling and using bolts would cause less stress than the other method, all I know is that it works on my boat, which is the same as on Mike W's, and the Shaggy guys did the same on theirs and they have no problems with it.
I use a big but stainless fender washer to spread out the load and minimize the stressrisers.
All I can say is that in 3 years, this has worked fine for me. Not saying that this is tyhe best method, just saying that it's an option that works.
martin a.k.a. the great gonzo!
Everyone must believe in something. I believe I'll go canoeing - Henry David Thoreau
we drill boats all of the time, mainly for kayak foot rests(I understand this is a les stress situation than thigh strap anchors, but same principle...), which I have had to do like 20 times in the last 3 weeks with all the new boats our program has gotten, and you will be fine to drill, I would just make sure to have the holes go around a structural bend, as in ideally not the same plane, if you can cross a curve you will have more strength, as the bend in a composite material is where all the structure lies. you don't need to tape, all you gots to do is just give er with a drill. and you will be fine, i recomment a slightly smaller bit than the bolt, and sand it or wiggle the drill to fit. and get the bolts wicked tight. I have never used lock-tite on a boat, but that would be an idea to consider, I know there are waterproof versions available now. also, if you can, go close to the seam as that is the strongest part of the boat... when I do all my strap anchors, they are right either on, or just next to the seam with some of my material overlapping the seam to get aqs much saturation as possible. I hope this helps.
cheers and congrats on the new Sith, I think that when I can, I would like to try to get one of those, but with the new race boats, that is a way off...
Skaal
-Isaac
race boats are so fast, i bet its in the speed wing.
For drain plugs I would recommend a big wood bit or a Forstner bit for the main hole, but a metal bit might work OK. Some resin on the edges of the hole would be nice. If you use the Harmony kit with the expanding rubber inserts, do check for delamination between the main drain hole and the smaller holes that receive the rubber inserts. Perhaps you could avoid the insert screws by glueing the drain plug housing to the deck with epoxy or a urethane glue.
I REALLY do not want to drill holes in this boat. I like to glass in rope. It's strong & looks real cool if you take your time & get it right (frayed red rope under s-glass) Thing is, there is a lot of flex where I want to glass in the anchors. I'm afraid I'll snatch a hole in the deck when playing hard. To give an idea of the lay-up, the boat weighs 20lbs
There's an extra layer of Kevlar in the flat spot that every other Sith has the straps bolted to. There is a lot of curvature for additional strength there too. This spot feels a lot stronger than where I'd have to glass in anchors.
There is no need to drill holes in a boat to attach thigh strap anchors.
We have been using this method for approx 30+ years.
1. Dry fit your seat and knee pads in the boat (do not glue them)
2. get in
3. grab your strap material (my favorite has always been 2 inch single webbing (not tube webbing)...kinda like stiff seat belt webbing
4. place the strap webbing over your thighs so it hits you on the thigh and at the angles (top and bottom) you prefer
5. grab the magic marker that you have laying on the floor beside you.
6. Elective step ( I tape the strap to my leg in the desired position)
6. Take the strap down to the desired anchor point between your legs and mark the spot with the marker (note angle and point of contact are critical) I usually mark a 2 inch wide mark on the bottom so I get the angle and placement correct). Also note that you may want to actually place the anchor point up under your leg somewhat so when you ultimately draw the straps down you draw your knees apart.
7. now position the strap at the back anchor point and mark the top of the boat where you want the anchor point to be (don't worry about marking your deck, light solvent will remove the marker
8. repeat on other leg
9. Get out
10. Remove seat and knee pads
11. Get some nylon braided climbing rope (here's your chance to add some flair to your anchors as climbing rope comes in cool colors
12. Cut the climbing rope in the follow length 2 inches for fraying, 2.5 inches for the strap, another 2 inches for fraying
13. with vinyl tape come in the 2 inches from each end and take a couple of turns around the rope.
14. you now have 4 ropes cut to these dimensions with tape on each side and a 2.5 inch middle section
15 fray the rope back to the tape (ie fray it 2 inches) fray it well your done with your anchors for now
16. cut out squares of some sort of boat making cloth (make sure the squares are large enough to cover the frayed rope when it is fanned out...think spreading the fingers on your hand) could be kevlar or glass..probably would not use carbon
17. cut a slit in one side of the square too the middle of the square
18. you now have your anchors and the anchor covers. you will need 8 anchor covers
19. cut out swatchs of peel ply that are larger than the squares you just cut..once again make the side to center cut
20. position your frayed rope on the bottom of the boat in the desired position (you can generally do both bottom anchors at the same time) remember to put a little bend in the rope so it sticks up a little from the bottom..otherwise you won't be able to get your webbing through
21. work the squares of material over the frayed rope so it covers all of the frayed area of the rope
22 dribble resin over the frayed rope and square combo...don't pour the resin on, but don't bee too conservative either...resin has a tendancy to take a while to run in, so be patient...I usually work it in with my hands as well..try not to touch the frayed rope as it will stick to your hands and mess up placement and hopefully it's fully coverd by the cloth squares you cut
NOTE 1: Might need to scuff up the area of the hull where you are putting the anchors with a little sandpaper
NOTE 2: Always wear latex golves and a good respirator when working with Epoxy..Davey sells a great respirator I use it for a lot of stuff around the house
23. put peel ply over the whole affair..work the peel ply into the frayed rope and anchor square to work out any bubbles and flatten out the rope the best you can..don't completely flatten it out as you want to leave some resin in with the frayed rope and squares
24. go watch slalom racing videos for 24 hours
25. pull off the peel ply and you should have a great anchor
26 for the top anchors, I turn the boat upside down...hang it from the ceiling with fore and aft ropes around the hull.... that way you can twist the boat to make the anchor level...you want to minimize the amount the resin runs.
logical queation time: Dave, you told us to put the mark on the outside of the hull, how do I know where to put my mark on the inside of the hull...2 ways...if the boat is light colored, you can see your mark if you hold a light on the outside and look inside the hull 2. good old fashioned measuring..I use a "T" square.
NOTE 3: If your boat is an extremely light layup, just make the frayed portion of the rope much larger and therefore you will distribute the load over a greater area.
Hope this is helpfull.
I always thought the object was to avoid getting holes in your boat...I struggle with that, I'm surely not going to purposefully put a hole in my boat....but I acknowledge I am older than old school...<grin>....DM
Picked up this method from Eric Amason for anchors. Instead of rope, pick yourself up some turnbuckles at the hardware store large enough to pass the 2" webbing through. Now cut yourself some strips of kevlar, two for each turnbuckle. Then cut another larger patch to cover the entire area around each turnbuckle. Slice these larger patches in the middle so the turnbuckle can poke through.
Test-fit and establish your placement, then mark your anchors with a sharpie. Hot glue your turnbuckle anchors in, then lay your two thin strips through the turnbuckles to form an X using West Systems as a resin. Now lay your larger reinforcement patch over your anchors. Cover the entire patches with duct tape, including the area through the turnbuckles to give it a smooth finish.
Let cure, finish outfitting and you've got yourself bomber anchors that let the webbing pass much easier than rope anchors.
I am personally a fan of the spectra or Nylon rope below kevlar for my anchors, but there are a variety of flavors... things work well for different people.
bananas
-isaac
race boats are so fast, i bet its in the speed wing.
I worked on the Sith tonight. The place I'd have to glass anchors is just too light. In the big, flat area I can flex it w/ my pinky. I don't know what the weight is on Martin's boat, but I have mine & Griff's here. I put them on the scale, Griff's is 30lbs & mine is 20lbs. The spot where everyone else bolts to feels very strong. I really do appreciate everyone's input. As bad as I hate putting holes in a boat (always thought it was stupid), and this is the first boat that I've ever had built, I'm going to bolt in this lap-belt.
Mike, My boat is similar in weight than yours, ~20 lbs befor I put any outfitting in.
Not sure where you intend on installing your anchors, but for me doing the m as recommended by the shaggy guys works fine.
As to the weitght of gridffs boat, I think they put some additional reinforcement into his boat since he uses his apparently for creeking ...
Since I have really long legs (36" inseam) I did not even need a bulkhead in mine, just foamed out the area around the bow pillars a bit, et voila, done! ...
martin a.k.a. the great gonzo!
Everyone must believe in something. I believe I'll go canoeing - Henry David Thoreau
I was going to glass in the upper strap anchors, but it's a VERY light lay-up 
& I'm scared it won't take the stress 
There's extra Kevlar on the flats so I guess I'll just have to drill holes & mount the straps w/ bolts. I've never drilled into a composite anything & was wondering what to look out for. Should I center punch it? Start w/ a small hole? Put masking tape on prior to drilling? The lay-up is Kevlar/glass/Kevlar.
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