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Old 14-01-2015, 09:07   #16
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Re: Proper support under deck stepped mast.

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This is yet another example of it.
And so it never ends.
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Old 14-01-2015, 09:23   #17
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Re: Proper support under deck stepped mast.

Easiest way to think this is to remember the old term from wooden boats - It was called the 'ring frame' It connects mast, chain plates and keel to make a structure that transmits all the sailing loads. The 'keel' as in the central beam that runs down the length of the ship is then a beam with the fore and back stays attached at the ends. This gives the essential engineering structure of a sailboat. The rest of the hull is there to create cargo space and keep the water out. Generally using wooden beams to spread the mast load caused problems as wood creeps over time if continuously loaded however heavy it is, engineered beams do better. Nowadays small yachts generally use a plywood bulkhead with a door. If you go that route be aware of the load when you look at the thickness above the door. The other common issue on fiberglass boats is the bulkhead distorting the hull. Needs to be well bonded in with plenty of extra laminate to spred the load away from the contact point. Hope this helps
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Old 14-01-2015, 09:28   #18
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Re: Proper support under deck stepped mast.

As a PS also remember that a sailboat fly's 2 'wings'. The sails fly in the air but the keel is flying through the water below. These two balance so must take very similar loads. This is in addition to compression loads. You need to be thinking in terms of several factors of the strength of the mast.
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Old 14-01-2015, 09:38   #19
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Re: Proper support under deck stepped mast.

As others have noted - you can't get away with violating the laws of physics. My 1962 Pearson Triton mast is deck stepped. Under it is a beam about 2"X3" that runs from side to side in the cabin. It also has a ss plate bolted to it that runs across the doorway made by 2 bulkheads that support the beam. The bulkheads serve to limit "panting" where the hull moves relative to the deck and cabin. Think of gussets in the steel fabrication world. You can't get away with just putting a support under where the mast is. You must direct the compression forces and control the flexing of the hull.

Whatever structure you see in the boat was put there for a reason.
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Old 14-01-2015, 09:50   #20
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Re: Proper support under deck stepped mast.

Thank you Crazyoldboatguy, but the structure that was put there was not original... And on top of that had had its lower half sitting in water from the hatch being left open. It had to go. I have come up with a good design for a new support, and I believe it will spread the load just fine. I wish I could post a pic of what I'm talking about..this app does not allow me to. Thanks to all for the advice. It is very helpful indeed!

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Old 14-01-2015, 10:16   #21
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Re: Proper support under deck stepped mast.

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Thank you Crazyoldboatguy, but the structure that was put there was not original... And on top of that had had its lower half sitting in water from the hatch being left open. It had to go. I have come up with a good design for a new support, and I believe it will spread the load just fine. I wish I could post a pic of what I'm talking about..this app does not allow me to. Thanks to all for the advice. It is very helpful indeed!

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So are you thinking of buttressing it around the cabin doorway? That might be neat.
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Old 14-01-2015, 11:42   #22
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Re: Proper support under deck stepped mast.

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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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Bad idea. The MFG would have done that for easy movement.
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Old 14-01-2015, 12:39   #23
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Re: Proper support under deck stepped mast.

Cadence? The original set up 42 years ago was a half bulkhead with a short 90 degree return. That was Irwin's design...I guess. I'll be distributing the load equally and with a lot less wood than the previous owner had overbuilt..in my opinion. I imagine that would have thrown off the way the boat handles. There was probably an easy 200 pounds of slimy plywood and untreated 2x4s that is now firewood. My final design will accomplish the task at hand just fine...and look good to...again thank everyone for their feedback, I'm sure I'll have many more questions for you all.

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Old 14-01-2015, 13:32   #24
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Re: Proper support under deck stepped mast.

Hi. I have an H28 1977 The deck under the mast started to deflect downwards. the owner about 15yrs back sandwiched the lateral deck beam under the mast with two 10mm by 150mm steel plates cut to the profile of the underside of the deck and traversing the width of the boat : carrying the load to the hull. All good now.
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Old 14-01-2015, 13:51   #25
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Re: Proper support under deck stepped mast.

Hey Barkie..I am going to incorporate plate steel into my design, along with good wood joinery. I am satisfied with my design.. As soon as I build and install it I'll try to upload a picture...but still don't know how to do that from this app.

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Old 14-01-2015, 14:15   #26
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Re: Proper support under deck stepped mast.

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...I am going to incorporate plate steel into my design, along with good wood joinery. I am satisfied with my design.. As soon as I build and install it I'll try to upload a picture...
You'd be much better served to post a sketch of your proposed solution BEFORE building it.
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Old 14-01-2015, 14:28   #27
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Re: Proper support under deck stepped mast.

TerraNova.. I can't figure out how to post any picture from this app. Otherwise I would be glad to do so.

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Old 14-01-2015, 19:02   #28
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Re: Proper support under deck stepped mast.

Can't help you with the apps.
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Old 14-01-2015, 19:22   #29
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Re: Proper support under deck stepped mast.

You know its the strangest thing. I've been combing over pictures of 73' Irwin28s, and I cannot find a good picture showing what is supporting the deck stepped mast. I did find schematics for a 28 and a 30. The 30 clearly shows what they designate as a "support pipe". The 20 shows absolutely nothing...no "support pipe". Does anyone out there own a 1973 Irwin28? If so what is supporting your mast?? If I get no direct feedback to my question, then I am going to have to build a doorway/support to do the job.

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Old 14-01-2015, 20:33   #30
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Re: Proper support under deck stepped mast.

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Originally Posted by Shawn Fitz72 View Post
I cannot find a good picture showing what is supporting the deck stepped mast...
Just Google Irwin 28 sailboat images.

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