A sailboat project....thoughts?

[MikeR]

As I said in my initial post, I work in the sailboat industry doing rigging and other obscure boat jobs.

I currently have a customer with the following problem:

1. Mast is aluminium.
2. Mast step (where the bottom of the mast rests) is steel.
3. Mast step is in the bilge and is in contact with salt water most of the time.

Steel-Aluminium in the presence of salt water sets up a battery like situation and the bottom of the mast (less noble) is beginning to corrode.

Here's what I'm considering:

Built a 'platform' from end grain white oak upon which to place the existing mast step. This will raise it out of the water. This platform will be 2.25" high.
Remove the same amount from the base of the mast so that all the rigging wires will fit. (Don't want to have to replace them, that's a $2,000 job).

The mast weighs about 200lbs but the total compression load due to other forces will measure in the nine thousand pound range. The finished platform will be 7"x19" and there won't be any point loading. (It's essentially flat).

I'm wondering what the collective wisdom of the group is relative to this solution.

Looking for some 'different perspective' suggestions.

Cheers,

MikeR

[MikeR]

A follow up

From Samuel J. Records study "Mechanical Properties of Wood", compression strength of white oak parallel to grain is 3520 lbs/ sq inch. Given that the platform will be 133 sq inches, it should support 468,160 lbs.

By the way, I plan on using smallish individual pieces, say 2"x2" epoxied together with a band of XGlass epoxied around the perimeter to keep the whole mess in one piece.

Thoughts?

Cheers,

MikeR

[lcm1947]

Hey Mike. I'm no engineer or even big brain but I am a sailor and have been for about 12 years now and that's why the word sail caught my attention. Having been around sail boats and being somewhat familiar with the forces that wind has on them I'd be very cautious about doing that. Now I am an overkill kind of guy so may just be being overly cautious here but I'd be talking to the boat manufacturer before even thinking about that. There are several reasons I say that but the imagine that really scares me is of that boat heeled over in a storm with the tremendous wind forces hammering, hammering and hammering that mast for hours. Anyway, I may just be being an old lady but it scares the crap out of me. Please check with the boat manufacturer.

[MikeR]

Hey Mike. I'm no engineer or even big brain but I am a sailor and have been for about 12 years now and that's why the word sail caught my attention. Having been around sail boats and being somewhat familiar with the forces that wind has on them I'd be very cautious about doing that. Now I am an overkill kind of guy so may just be being overly cautious here but I'd be talking to the boat manufacturer before even thinking about that. There are several reasons I say that but the imagine that really scares me is of that boat heeled over in a storm with the tremendous wind forces hammering, hammering and hammering that mast for hours. Anyway, I may just be being an old lady but it scares the crap out of me. Please check with the boat manufacturer.

Hey, since you're from Austin, do you sail on Lake Travis? We took my son's j80 down there last year and it was awesome to sail right up to the cliffs and hold over 100 feet of water.

As far as the mast step is concerned, others have built up steps using fiberglass. Glass is very strong in tension but not so much in compression so my logic is that the oak which is very strong in compression would work well.

I'll post photos as I go along to show how it will work.

By the way, boat manufacturer has been out of business for 20 years (Pearson) but I've done and re-done lots of rigging and totally understand the forces that can be generated.

Cheers,

MikeR

[backpacker85]

Mike-

Just my 2-cents, and only unprofessional opinions, but...

While I think your fix would work, I would not really be comfortable with what amounts to an extra "joint" at the base of the mast. Even with a keel-stepped mast, shimmed & secured where it penetrates the cabin roof, you can get a good bit of sideways load at the base when the mast flexes.

My first choice would be to remove the steel mast step and replace it with an aluminum one, but this may not be possible if cast in fiberglass.

If that isn't possible, since it sounds like the base is going to be submerged, would be to skip the oak and use lignum vitae, which is much more dense & frequently used in underwater applications.

Hope this helps a little...

BTW....used to do a good bit of sailboat racing in your area (and beyond) when I "spent a few years" at KP in Great Neck....loved the area.

[MikeR]

Mike-

Just my 2-cents, and only unprofessional opinions, but...

While I think your fix would work, I would not really be comfortable with what amounts to an extra "joint" at the base of the mast. Even with a keel-stepped mast, shimmed & secured where it penetrates the cabin roof, you can get a good bit of sideways load at the base when the mast flexes.

My first choice would be to remove the steel mast step and replace it with an aluminum one, but this may not be possible if cast in fiberglass.

If that isn't possible, since it sounds like the base is going to be submerged, would be to skip the oak and use lignum vitae, which is much more dense & frequently used in underwater applications.

Hope this helps a little...

BTW....used to do a good bit of sailboat racing in your area (and beyond) when I "spent a few years" at KP in Great Neck....loved the area.

We sail in Little Neck Bay and are very close to the guys up at KP. In fact, our daughter is getting married next May at the O Club.

The mast step is held in place with 4 1/2" SS bolts so thwartship movement is not a problem. I like the lignum idea though.

Cheers,

MikeR

[LowerUnit]

Please forgive my ignorance, but why can't this area of the boat be kept dry and free from water?

I am in the boat repair industry myself and my thoughts tell me to eliminate water intrusion to minimize the impact of water/saltwater exposure.

I should point out that I've only repaired some minor electrical or engine mechanical problems on a few sailboats and that I'm much more proficient and knowledgeable about powerboats.

[MikeR]

Unfortunately the boat has relatively shallow bilges and the small amount of water that gets in through the stuffing box settles in the way of the mast step. Just a function of the profile of the hull.

Cheers,

MikeR

[lcm1947]

J80, you said? Nice! Yes, we've sailed Lake Travis for 12 years now and she is a beautiful lake - and yes indeed deep although she's down about 30 feet right now. We, meaning my wife and I have had a 27' Catalina for the past 6 or 7 years and just about sailed Travis to dealth. Sorry if it seemed I was questioning your boating knowledge but I didn't know how experienced you were, but now I see that you're no newbie at it so yeah keep us posted with plenty of pictures please. Good luck.

[MikeR]

We certainly enjoyed our visit and the racing.

I've got over 50 years on the water, loving every minute of it but have reached the point where the body isn't as willing as the spirit so will have to be content with sailing our own boat and not racing with the kiddies.

They live in Annapolis and trail the j80 all over the country to race it. They're leaving in two weeks for Key West Race Week. I've done it twice and can say that its about the nicest place in the world to sail.

I've also done a lot of work on C27s in addition to the 25s and 30s. They are terrific boats, very comfortable with a good turn of speed.

Will keep you posted and post some photos.

Cheers,

MikeR

[lcm1947]

Yeah Mike I know the feeling about the mind willing but not the body. My wife and I are currently thinking about selling her, the boat not my wife. Sailing is a life style and you have to be willing to devote just about every free minute to it. So we are thinking about it anyway, but just one more summer of sailing sounds good to us though.

[big tim]

mast base

I had to replace the mast sub base on my ketch this winter, not because of eletrolycis, but because of dry rot in the teak sub base.
I wouldn't wory about compression strength, but more about rot. I also wouldn't use endgrain. The teak sub base was in my boat for 22 years and there's absolutely no evidence of any compression in the old base. The boat is 40ft long and the mast is a heavy 55ft aluminum extrusion(11" x 7.5" oval in cross section).
The mast is stepped on the aluminum plate which sits on the teak sub base which sits on a very heavy fibreglass pedestal which in turn sits on the keel, no bilge water to wory about.
The picture shows the old teak sub base on the left and the new one in the middle.
I don't see anything wrong with what you are trying to do, other than that endgrain business. It would be nice if you could get that mastbase up more out of bilgewater. I'm rather surprised that they used a steel maststep. Maybe you can replace it with an aluminum one.
Good luck

Tim

http://i129.photobucket.com/albums/p...ift/Pic992.jpg

[MikeR]

Hi Tim-

I wonder why you say that about endgrain? My sense is that that orientation is where the wood has the highest compression strength.

Northeastern boat builders (Pearson) did some strange things, like the steel mast step. On the other hand the glass work was tremendous. My boat, for example, has 1" laminate at the turn of the bilge an no core anywhere in sight.

Also, I believe that white oak is extremely rot resistant. At the place where I volunteer, Rocking the Boat (www.rockingtheboat.org), we've built 16 Whitehall rowing boats using steam bent white oak for all the structural components and they sit in salt water most of the time.

With thanks for your insights.

Cheers,

MikeR

[big tim]

The reason I mentioned about endgrain is because that way more endgrain is exposed to water. It's my understanding that water enters wood more readily via the endgrain then through the walls of the wood fibres.
In wooden boat construction you go through great pains to avoid exposing end grain to water.
As I mentioned in my previous post you really don't have to worry about the compression strength of the wood. I'm assuming of course that the buttend of the mast has a metal shoe on it, distributing the weight rather than that rim of the mast is sitting directly on the wooden mast step.
Anyway my two cents worth.

Tim

[jrnewhall]

MikeR.

I've been racing boats for 20+ yrs and sailing all of my life. I've done my share of repairs on older boats over the year. Mast steps can take some very tough beatings in a all directions; tremendous compression especially if this boat has an adjustable backstay and considerable leverage side to side. Think of rounding up with the spinnaker up and the loads distributed throughout the rigging and down to the step as the spinnaker flogs the fills.

I wouldn't worry about redesigning the mast step. Besides, there are all sorts of other metals screwed into the mast and I don't think you can keep the mast dry. I think you should look at the electrolysis from a different angle. By the way, does the mast show signs of electrolysis? You could just attach a zinc at the base. You my want to check in some riggers reference but I think if there is a zinc in the water and everything is electrically connected, you shouldn't have too much of a problem. You just have to remember to replace the zinc every year or two.

~JRN