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  #1  
Old 05-07-2013
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Step Mast holes stripped

Hi. Have a US Yacht 25. Mast is down. Thought I'd check and re-do the mast plate to hull connection.

There are 4 bolts that connect stepplate to hull. The way I removed them, two forward longer bolts, two smaller aft bolts.

The two aft holes (not the bolts) are both stripped. Not sure how long it's
been this way or if I caused.

Is there a metal base below topside that the stepplate bolts to? To me, it
looks like it's just the fiberglass hull threaded to accept these (machine S.S.) bolts. Or perhaps a heli-coil of some sort in the hull?

To fix. Can I just tap a slightly bigger hole, using normal tap/die equipment,
then oversize the machine bolt (will have to enlarge the metal stepplate also to accept the new bolt). Or perhaps clean hole, fill with resin and redrill/tap to original size?

This is a 1982 sailboat. Is it normal for the mast step bolts to bolt directly into the fiberglass hull?

I realize this is a critical aspect of the boat. Do want to get it right.

Thanks again,

Chris
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Old 05-07-2013
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Re: Step Mast holes stripped

Quote:
Originally Posted by budvar View Post
Hi. Have a US Yacht 25. Mast is down. Thought I'd check and re-do the mast plate to hull connection.

There are 4 bolts that connect stepplate to hull. The way I removed them, two forward longer bolts, two smaller aft bolts.

The two aft holes (not the bolts) are both stripped. Not sure how long it's
been this way or if I caused.

Is there a metal base below topside that the stepplate bolts to? To me, it
looks like it's just the fiberglass hull threaded to accept these (machine S.S.) bolts. Or perhaps a heli-coil of some sort in the hull?

To fix. Can I just tap a slightly bigger hole, using normal tap/die equipment,
then oversize the machine bolt (will have to enlarge the metal stepplate also to accept the new bolt). Or perhaps clean hole, fill with resin and redrill/tap to original size?

This is a 1982 sailboat. Is it normal for the mast step bolts to bolt directly into the fiberglass hull?

I realize this is a critical aspect of the boat. Do want to get it right.

Thanks again,

Chris
I wouldn't worry too much about it. Very often steps are bolted down with lags.
I think I would just fill the holes with resin or epoxy and either drill the same place for the new bolts or just drill in fresh places. Very likely, you could just get the next size larger lag bolt.
There is virtually no chance that the step is going to go anywhere when you get the compression of the mast pushing down on it. The bolts are there mostly just to locate the step.
The most critical aspect of it is to keep the corrosion from eating the step and bolts.
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Re: Step Mast holes stripped

I'm confused. You mention "4 bolts", but also mention that the holes the bolts go into are stripped. I'm not a machinist, so take my answer with a grain of salt. But I thought a bolt was something that went through the materials to be held, and had a nut or other fastener on the other side. It is this fastener that actually does all the "holding". This is in contrast to a screw, which bites into at least one of the materials to be held, thus making the material itself the fastener. With that as background, if you have screws holding your mast step in place, and if two of the screws are stripped, you'll want to do a careful repair of that area. If it is bolted, then I wouldn't have quite the same level of concern, but you'll still need to carefully repair as this is a critical area of the boat. You'll want to see if the core (probably plywood) is rotten in that area, and clean that up.

Check out Maine Sail's website; he has great information about these kinds of repairs.
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Re: Step Mast holes stripped

Jimgo.. you can thread the plate you're bolting to and 'nuts' are not necessary.. I suspect that's what's been done here, but usually I'd expect a metal plate to be embedded into the deck and the bolts threaded into that. However as Knothead indicated there's very little load on those fastenings, if any at all.. the mast compression is going to hold everything down and the 'bolts' are little more than pins to locate the step and discourage any lateral movement. I've seen bolts threaded into fiberglass before on such low load applications.
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Re: Step Mast holes stripped

Faster,
Good point about tapping the plate. However, in this case wouldn't the step be sitting on top of the deck? So the bolt goes through the plate, then into the deck. His bolt would still be biting into wood which has stripped.

As to the load on the step, this is likely my ignorance showing through, but don't you have both compression and shearing forces there. I guess, even with shear, the bolts just need to not work free; it's not like the mast is suspending the boat ( though I have seen that done).
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Re: Step Mast holes stripped

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Originally Posted by jimgo View Post
Faster,
Good point about tapping the plate. However, in this case wouldn't the step be sitting on top of the deck? So the bolt goes through the plate, then into the deck. His bolt would still be biting into wood which has stripped.
I guess I wasn't very clear.. the mast step plate would be drilled for clearance, not tapped. But a drilled and threaded plate could have been embedded in the deck during layup, and the step plate bolts threaded into that, avoiding visible 'nuts' on the inside of the boat. It sounds like here the fiberglass deck was itself threaded to accept the step plate bolts.. f/g actually takes a thread quite nicely but it's not all that strong. In this case someone overtightened the bolts and stripped the holes out..
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Re: Step Mast holes stripped

I was half asleep this morning when I read the op. I was thinking that he was talking about a keel stepped mast.
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Re: Step Mast holes stripped

Thank You all! Correct about the "machine screws", not "bolts". You've given me some good feedback, and refilling with resin or tap a larger hole sound like nice options. I would feel better if there was a plate to thru bolt to. However, it is helpful to hear that the loads placed on the mast plate/hull are not extreme.
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Re: Step Mast holes stripped

Wonder if you could coat the "machine screws" with some sort of release agent. Then fill
in the holes with epoxy, jam the "machine screws" into the hole just filled with epoxy. Let the epoxy setup, then back out the "machine screws". TA-DA.......threads are formed by the epoxy. Would this work? Saves the trouble of getting a tap, drilling the right size hole, taping the epoxy (don't know how that goes), cleaning out the hole, ect ect.
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Old 05-17-2013
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Re: Step Mast holes stripped

Thanks to all here and elsewhere for listening, and for solutions. I ended up using advice from an article on this old boat. Here is what I did:

I learned volumes on this project. Borrowed a bit from another forum on sailnet.com.

Short story: US Yacht 25. Mast down, replacing standingrigging. Checked the mast step, had 4 machine bolts into deck, two of the holes were stripped. The holes were into the decking/plywood sandwich. No backing plate.

I prepared to fill the hole with epoxy, then retap. But wait.....epoxy makes a weak thread. Wouldn't it strip again?

Found an old article on sailnet.com. Someone had a similar problem. One person theorized that setting a hex coupling in epoxy would be the solution.

I went around town, found one SS coupling, then went to another local Co. they had a smaller coupling (necessary as the US Yacht mast base bolts are less then 1.25" then you open a hole into the head!).

Long story short: oversized the mast step bolt holes to 7/8" or so. One hole when thru to the "head" (covered hole with duck tape per dude on Compass Marine). Ended up being 5/16 hex coupling. Used a flat head screw on bottom of coupling to help keep intact and from crawling up when tightened, if that makes sense, please see pictures.

Friend of mine recommended roughing up the SS so the epoxy has something to grip on. The rest I did as per Compass Marine.

It worked! Now this should be an improvement on the original, that is real threads for the mast step to grip on.

Hope this helps, I learned volumes by doing this, couldn't have done without the help here and from Sail.net.

Unable to post pictures, sorry, it won't let me. they are on baylinerbuccaneergroup.
Chris
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