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Old 13-01-2015, 05:51   #1
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Proper support under deck stepped mast.

I have recently purchased a 1973 Irwen28. This boat was abandoned and I got it for $200. Previous owner had done some plywood work in the interior. The boat was flooded with rain water, due to the hatch being left wide open. I pumped all water out, and demoed all plywood that was soaking in this water. There was a rather over built doorway located right under the deck stepped mast. I removed all of this structure..but I had a feeling that something wasn't right...due to backstay getting slack all of a sudden. I have jacked up a 4x4 temporarily. Please someone let me know what I should do here. I am a fabricator, and can build most anything...but I don't want to over build something like what was there. I have researched original photos, and only see a half bulkhead with a short return wall I guess to be supporting the mast..it looks flimsy to me. Any help would be greatly appreciated. Thank you

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Old 13-01-2015, 09:44   #2
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Re: Proper support under deck stepped mast.

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Originally Posted by Shawn Fitz72 View Post
I have recently purchased a 1973 Irwen28. This boat was abandoned and I got it for $200...
There was a rather over built doorway located right under the deck stepped mast. I removed all of this structure..but I had a feeling that something wasn't right...due to backstay getting slack all of a sudden...
Doh!

What did you expect would happen?
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Old 13-01-2015, 10:04   #3
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Re: Proper support under deck stepped mast.

It wasn't "overbuilt". It had a purpose which made itself clear to you when the rigging sagged. Put it back. That area MUST be supported to maintain deck and hull integrity under the pressure of the mast.
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Old 13-01-2015, 10:07   #4
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Re: Proper support under deck stepped mast.

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Please someone let me know what I should do here. I am a fabricator, and can build most anything...but I don't want to over build something like what was there.
Larger boats with a deck stepped mast generally have a metal compression post that goes from under the mast to the hull to provide deck support. Assuming the original support is not usable any more, and not knowing your exact interior design, a correct length of stainless or aluminum tube with fabricated flanges on both ends might be an easier, suitable replacement. You could then decide if, aesthetically, it makes sense to address the finish on the metal or to enclose it in bulkhead trimmings. Getting the height correct will probably require a little leg work. I would thank that, at the least, you would need to slacken all the rigging to get the deck to pop back up, if not lifting the mast a bit.
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Old 13-01-2015, 10:12   #5
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Re: Proper support under deck stepped mast.

I guess I didn't know what to expect...I've never owned a sailboat, but logic did kick in and I put a temporary support up. The structure that was built was bulky to say the least and not engineered correctly..in my opinion. No harm was done and I do plan on rebuilding a better engineered system. The original support had long been gone, and was in no way built like what I removed..there had to have been a couple of hundred pounds of laminated beam and 2x4s. It was the right thing to do, seeing that this structures lower have had been submerged in rain water for some time.

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Old 13-01-2015, 10:22   #6
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Re: Proper support under deck stepped mast.

Thank you Garrets. I have thought of a compression pole of some type, but I'm opting for more ease of movement through the cabin. So I'm probably going to build a doorway/header to disperse the load evenly to the floor. This boat has a fiberglass insert. I've looked under the floor to find the structure would lay upon stringers and I will attach to plywood bulkheads and returns.

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Old 13-01-2015, 10:27   #7
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Re: Proper support under deck stepped mast.

I'm using the CF app and don't know how to upload a picture. If this can be done, please let me know. I can show original support and what was put up much later. It might help.

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Old 13-01-2015, 10:37   #8
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Re: Proper support under deck stepped mast.

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Originally Posted by Terra Nova View Post
Doh!

What did you expect would happen?
Now put back what you took out!
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Old 13-01-2015, 10:48   #9
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Re: Proper support under deck stepped mast.

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Originally Posted by Terra Nova View Post
Doh!

What did you expect would happen?
I don't see how this can help the OP.

Shawn - as stated above, the compression post is needed to spread the load over the deck and hull. Usually this is done by a glassed-in bulkhead extending to both sides of the hull and heavier FG layup under the deck. Some boats have a compression post sitting on the keel, but you still need to reinforce the hull sides to account for the inward pull of the shrouds. This not only to keep the fore and back stays taut but also when sailing the force on the sails make the mast push downwards on the mast step, and when going to windward it sometimes has a pumping action - which also calls for a strong mast step on the deck to prevent if from moving sideways or for and aft, keep this in mind when rebuilding.

Here is further information - for a CAL 28:

Mast Compression Fix on Cal 28 - Boat Design Forums

Mast Compression Fix on Cal 28 - Page 2 - Boat Design Forums
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Old 13-01-2015, 10:59   #10
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Re: Proper support under deck stepped mast.

Thank you SVTatia! That's the kind of response I'm looking for.

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Old 13-01-2015, 11:25   #11
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Re: Proper support under deck stepped mast.

The FIRST thing to do is slacken all the standing rigging off a bit, to take some of the load off the deck, until you repair it better.
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Old 13-01-2015, 11:48   #12
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Re: Proper support under deck stepped mast.

PS, I'm not sure you appreciate the load you need to design for. The rigging is normally tensioned for 15% of breaking point. If you add the forestay, backstay, and shroud tensions, and the weight of the mast, you could easily have 2500 lbs downward thrust on the mast, maybe a lot more. Measuring the standing rigging diameters and using the info at Loos Gauge will give you a baseline load. You want the minimum of flex in your structure, so it has to be pretty strong.

Issues with mast support structures are common, even when designed by the manufacturer. You really need to seriously consider how to do this job properly, because you don't want to be doing it twice.
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Old 13-01-2015, 12:26   #13
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Re: Proper support under deck stepped mast.

Thank you Market. I have come up at a design that I will believe to work while not being so overly bulky. Like I have stated previously, the original support was a plywood wall and a short 90 degree return. I am a woodworker and understand good joinery, and how a well built support/bulkhead will work. I really just wanted a little advice as to others have dealt with this issue...and I'm still open to ideas.

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Old 14-01-2015, 08:58   #14
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Re: Proper support under deck stepped mast.

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I don't see how this can help the OP.
It can't. It's just another comment from the Peanut Gallery. There is a lot of that here

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Old 14-01-2015, 09:02   #15
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Re: Proper support under deck stepped mast.

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It can't. It's just another comment from the Peanut Gallery. There is a lot of that here

This is yet another example of it.
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