H17 daggerboard rebuild

Hi, I am updating and rehabbing an H17 Sport. One of the projects is to rebuild the daggerboards. I have the idea to cut the tips off and recreate them using west system epoxy. Also use west system epoxy to reinforce the hooks with some cloth. Any one have any experience or suggestions?

Thanks,
Steve

See the articles on Hobie 17 centerboard repairs in the HOTLINE . . .

Part 1 - http://www.hcanamembers.com/13-1WinterHotline.pdf
Part 2 - http://www.hcanamembers.com/13-2Hotline.pdf

You need to use a spline to repair the tips - either a fiberglass or carbon sheet.

A carbon rod does a much better job of reinforcing the hooks - adding glass will make the hooks bigger and cause interference (the dimensional tolerances are quite small in the hook area).

Great articles. I need to get subscribed to the HOTLINE.

But I'm wondering if I need to go that far. My hooks aren't broken, but one does have a small stress crack. My idea was grind them down a little and use a couple of neatly trimmed pieces of cloth and west system epoxy, build them back up, then sand them down to the correct width.

My leading edges are wore and the two tips are shortened one more than the other. My idea here was to cut a slot down the leading edge, clean out the tips and rebuild them from the inside out using west system epoxy, adding cloth on the final layers.

I am experienced using west system products. Also I'm not worried about them being white in the end, only about them being robust enough to handle the beach.

Do you think this will work?

Thanks in advance for your advice.

Start here - http://www.regattanetwork.com/membermgm ... n_form.php

A $20 recreational / SUP membership is essentially a HOTLINE subscription.


The hook is the highest stress area on the whole board. The strength in it is not in the outer skin, but the glass rope that's laid into it during the manufacturing process. In the first article, there's a section called "Preemptive Repairs" that shows how to deal with this by inserting a carbon fiber rod into the backbone of the centerboard. It's cheap, easy and your hook will never break off.


There's no need to build up with cloth on the edges, unless the foam is exposed. It adds no strength and is only marginally abrasion resistant (which is what you need). Slot the edge and glue in a spline (either of glass carbon sheet) that's the original outline of the board and build up to it with WEST System thickened with colloidial silica (407) to a peanut butter consistency. The spline gives you a guide to shape the edge to.

BTW, WEST resin must be protected from UV, else it turns amber and gets brittle. That means painting or using pigment in the mix.

What great information. I signed up for the news letter yesterday.

The hooks on my boards aren't broke and look to be in pretty good condition except for what looks like a small stress cracks. Since you said the strength in the hook in from the inside, probably the case here is to fix them cosmetically.

I want to use a somewhat different method on the tips though. My idea is since the strength comes from the middle out to the walls, maybe I could cut out the exposed foam on the tips and preserve the walls. Then epoxy the sides together using 404 fillers for strength. Then I wouldn't have to cut the edges off.

Is there a place to host images so I can post them here?

If the gelcoat on the end of the hook is cracked, then likely the hook is on the verge of failing. There is fiberglass "rope" inside the hook which is what gives the hook its strength. The problem is that this rope does not extend all the way to the tip of the hook, it only goes to about the half way point of the hook. The rest of the hook is just putty/gelcoat which has very little strength. If the gelcoat is cracked at about the middle of the hook, I would not consider this cosmetic. I would consider this a warning sign that that the hook is probably getting ready to break off.

sm

Thanks for all the information on my project. But sometimes for me it's easier to talk about it than write it down. Please look at this.

https://www.youtube.com/watch?v=0VkxpPICwvI&list=UUuiIH1MiYgpEwkOljA7MOXA

Thanks for your input.

The reason those cracks are there is because the hooks are flexing - a prelude to breakage. THEY ARE NOT COSMETIC.

The carbon fiber rod is a stupid easy preventative repair to do - replacing a broken hook is a lot more work.

The spline method of repairing the tips / leading edge is the way to restore the boards to their original condition. Proven again and again. Don't try to reinvent the wheel. These repairs are not rocket surgery.

Look, you came here asking for advice. We gave it to you. I wrote the articles in the Hotline. I've been racing and repairing Hobie 17s for 25+ years. I'm a naval architect (engineer) and really good with fiberglass and WEST System. Steve Myer (srm) is an engineer and a really good fiberglass guy. If you don't want to take our advice, fine - but be prepared to live with the consequences.

scharrow you have been told mate, by the practicing, educated and experienced guru of H17's. You asked him for advice and responded with a meant-well video of a guy who doubtless thought he knew what he was about. By doing that you gave the video man the same credibility as MBounds. That was an error on your part as you might divine from Mr Bounds succinct comments.

It is your call - let your CB fail and fix it or take measures to protect it from failure. The video did not show you how to avoid fail.

If I gave you the idea that I wasn't going to fix the hooks with the information I got here, then I apologize. Since they are not broken totally off, then now is the time to get them done and to do them right. I made that short video just to clear up how my boards actually look. I'm sorry if I gave any notion that everything was good enough just the way it was.

Thanks for all the advice. I am trying to locate the carbon fiber rods locally now. I will report back here where how the repair is going.

The repair with the carbon sticks seems to be the best solution.
Could this also be a way to prevent the hook flexing?
The stainless steel piece can be filled up with Resin.
...just launching an idea.....

May keep the hook from flexing but the added thickness may cause an interference in the hook cavity in the hull.

Additionally, the aft two (certainly the aft one) attachment screws are going into mostly foam.

Bending stiffness is the product of the material's Young's Modulus and the area moment of inertia.

Stainless steel and carbon fiber rod have approximately the same Young's modulus - about 180 GPa (steel is a bit stiffer).

The real difference between the two reinforcements would lie in the area moments of their cross sections.
A 2 mm x 20 mm rectangle has an area moment of (20*2^3)/12 = 5.33 mm^4
A 9.525 mm diameter circle has an area moment of (pi/4) * r^4 = (3.1415/4)*(9.525/2)^4 = 404 mm^4

The carbon rod is a lot stiffer than the stainless strap. And a lot lighter, too.

Ya Ya Ya Young models, bending stiffness, moment of inertia. We get it matt! So childish

Hey, I gotta make my dad proud that he paid for that engineering degree I got 30+ years ago. I barely remember that stuff.

Everyone has to agree that the rods are the strongest and lightest solution. So I went to a local hobby shop looking for carbon fiber rods. The best thing they had was carbon fiber tubes that are used in model aircraft. The 10mm tubes were very stiff, very strong. And they wanted about 35 bucks for one also. I was almost ready to go that direction and buy them when I just for kicks tried to swing one like a golf club. A light went on and I thought the strongest carbon fiber tube would be a driver shaft. I went to my local pro shop and they had a couple of old extra stiff driver shafts. What makes a shaft extra stiff is the end is almost solid and they where 3/8. The tips of the shafts are very strong. Perfect fit. Perfect price. Free.

I am working on the daggerboard tips now. And by the way, both of my tips looked to be in great condition, but upon further review, they where both broken. Not just across the hook, but also cracked down the seam between the sides. Mr Bounds was totally right. Thank you sir.