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-   -   Tabernacled Keel Stepped Mast (https://www.sailnet.com/forums/boat-review-purchase-forum/75980-tabernacled-keel-stepped-mast.html)

hdra 07-06-2011 11:38 PM

Tabernacled Keel Stepped Mast
 
So I just went up to Santa Barbara today to look at this http://www.yachtworl...g_id=14024&url= islander 36. Everything on it seems pretty good, except for one big weirdness - Some prior owner took a perfectly good keel stepped mast, cut it in half at the deck, and installed a big aluminum plate as a tabernacle so they could raise and lower it. The lower section of the mast is still intact inside the boat, functioning as a compression post - the top of the bottom half of the mast goes through the partners and rests against this aluminum plate that they installed to hold the tabernacle. Now, my first thought was that this was pretty ridiculous, but am I right in thinking that this setup significantly weakens the mast? I like the rest of the boat, but I don't want to have the rig come down because someone took a sawzalll to it years ago. On a related note, does anyone have any references for how hard/how much it would cost to splice the mast back together again? Is that something even worth considering?
http://i1103.photobucket.com/albums/...s/IMG_7021.jpg
http://i1103.photobucket.com/albums/...s/IMG_7023.jpg

olson34 07-07-2011 10:46 AM

The spar was designed for a calculated stiffness, based on total length and support. One of the reasons that NA's like the keel-stepped spar is that weight is minimized and the section can be smaller for a given length.
At some point of stress, that shortened mast will fail, and fail sooner than the NA would have calculated for a stock boat.

Remember that the I-36 is an off shore cruiser/racer and built and rigged for that purpose. That's just one reason it is rightly referred to as a modern classic.

Hypothetically you can safely convert any keel stepped rig to a deck stepped, but you have to change the cabin/bulkhead engineering & structure midships and change the spar section... This is not cheap or easy.

Any knowledgeable surveyor will red-flag such a modification, unless there is actual certification that all the internal work was done and a new spar section was installed. (Possible, but rather unlikely.)

And then, way down the road, someday... if the rig/boat is damaged by sea or wind conditions, your insurance company will probably use that change as a huge loophole to disallow your claim and cancel your coverage.

And, As for splicing it back together, note that a section is missing. You would need the exact missing section, probably over a foot long, and then a plug to exactly match the inner shape. The section is probably not possible to find, after all these decades. :(

Better think twice before buying that boat. :rolleyes:


L

Tynesider 07-07-2011 11:51 AM

Hi Olsen
I tried to look at the boat your buying but the site comes up unobtainable.
However if it's a 36' boat then that Tabernackle sure looks a poor one from a build quality as there is no ties between the cheek plates and the bottom of the mast looks poorly connected to it and only with one bolt! I guess the mast on your new boat must be about 40' min.

My own Tabernackle on my CW 24' shown below is to my 30' mast manufactured out of Galvanised 3/8" plate and strengthened front and back as you can see, however even with a 30' mast it's best a crane job to lower it, so for a 36' yacht I do not see the point of why it was fitted.

As said why buy a future problem.

Mike

http://i370.photobucket.com/albums/o...Picture003.jpg
http://i370.photobucket.com/albums/o.../CaerUrfa2.jpg

landmineop 07-07-2011 07:44 PM

Tynesider
I am not at all familiar with Colvic Watson motorsailors. Untill your post I had not heard of them. AFTER, your post, the more I read about them the more I am impressed with them. The only fault I can find is that y'all seem to keep all of them across the pond. Give us a break ! Send a couple our way !

Tynesider 07-08-2011 06:14 AM

Quote:

Originally Posted by landmineop (Post 747855)
Tynesider
I am not at all familiar with Colvic Watson motorsailors. Untill your post I had not heard of them. AFTER, your post, the more I read about them the more I am impressed with them. The only fault I can find is that y'all seem to keep all of them across the pond. Give us a break ! Send a couple our way !

Hi Landmineop

The Colvic Watson Motorsailer has a pedigree second to none as they were designed by the 'first ever' Yacht designers G L Watson & Co when they were in Glasgow dating back to 1873, but the Colvic Watson's were designed in the 70's.

My own boat (23'-6") is a small one and the biggest is 34'-6", if ever you want to know more I wrote the History of the Colvic Watson Motor Sailer for the Colvic Watson Owners Group, if you PM me I can send a copy on line.
There are a couple your side of the pond.

Happy sailing days

christyleigh 07-08-2011 08:38 AM

Quote:

Originally Posted by Tynesider (Post 747958)
The Colvic Watson Motorsailer has a pedigree second to none

Hey Mike..... them's Fightin.... Words...... :D :D Just kidding ;) I don't know much history of the Nauticats (Finland) before the 70's but the original 33 that mine is the say... 3rd generation of, is also from the 70's.

Back on topic..... I agree that home made tabernacle in the O.P. is a poor effort. About 15 years ago I had a Nimble Arctic 25 Pilothouse trailer sailer (American made) that had what I considered to be the best tabernacled mast I've ever seen. It took yours one step further by also having a plate (the whole thing was beefy like yours) on the front above the pivot pin so that when it was lowered and the pivot pin was removed it was still totally captive in all directions. I used to raise and lower it myself although chances are good that the mast itself was not as beefy as yours. The tabernacle on the Nimble almost seemed out of place because it was such a massive piece of work. A nice little boat but from what I can see definitely not in the same class as yours.

svHyLyte 07-08-2011 09:51 AM

Quote:

Originally Posted by hdra (Post 747547)
So I just went up to Santa Barbara today to look at this islander 36. Everything on it seems pretty good, except for one big weirdness - Some prior owner took a perfectly good keel stepped mast, cut it in half at the deck, and installed a big aluminum plate as a tabernacle so they could raise and lower it. The lower section of the mast is still intact inside the boat, functioning as a compression post - the top of the bottom half of the mast goes through the partners and rests against this aluminum plate that they installed to hold the tabernacle. Now, my first thought was that this was pretty ridiculous, but am I right in thinking that this setup significantly weakens the mast? I like the rest of the boat, but I don't want to have the rig come down because someone took a sawzalll to it years ago...

I seem to recall sailing aboard a number of Islanders with deck-stepped masts while we lived in San Francisco. As I recall, the mast sections did not seem to be any heavier than did the sections on the keel stepped yachts and it's likely that Islander used the same mast on both versions of the boat. The only change in the structure of the mast is the "effective unsupported length" of the "column" between the deck and the lower spreaders in the calculation of Euler Buckling loads as the column (mast) goes from a fixed end condition to a pinned end. It is not a big deal to calculate the buckling loading if you can come up with the mast section and I suspect that would not be difficult (check RigRite). Further, I am reasonably confident that there is no problem.

In SoCal it was not uncommon to see yachts transformed from keel stepped masts to tabernacle based masts, particularly around Huntington Beach and Long Beach where there were/are relatively low fixed bridges between waterfront homes with docks and the ocean and it was not unusual to see a yacht with its mast angled forward at 45 or more to make it under these bridges (although this would be problematic with roller furling). In some respects, there is much to recommend the design in areas where there are low bridges. In my own case, it only takes one bridge less than 65' to make a section of the ICW entirely unusable.

I suggest you have a structural engineer take a look at your prospective yacht as you may/likely have a non-issue.

FWIW...

Tynesider 07-08-2011 04:01 PM

Quote:

Originally Posted by christyleigh (Post 747973)
Hey Mike..... them's Fightin.... Words...... :D :D Just kidding ;) I don't know much history of the Nauticats (Finland) before the 70's but the original 33 that mine is the say... 3rd generation of, is also from the 70's.

Hi Stan
Nice Motorsailer you have there!

I assume you have been on the Nauticat history site, you should know exactly when yours was built by the Hull Number.
Nauticat History

Regards
Mike

hdra 07-10-2011 04:42 PM

Thanks for all the input - in the end I've decided to stay away from the boat, as I don't need the tabernacle feature, so there's no point in adding complication and potential weakness without actually needing it.

deniseO30 07-10-2011 05:29 PM

Eh, I just don't think it was a reason to walk away. there are lots and lots of deck stepped mast boats out there. Maybe the whole boat was a collection of Half baked "improvements"?


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