Mast/Tabernacle Step

[glennk]

I'm in the process of replacing the false flooring (3/4" plywood) on my DS1. I had a few small leaks/holes beneath the floor and in trying to find them determined that it was just easier to replace the entire floor rather than to chop holes looking for leaks.

As part of that process I removed the 2"x4" that was bolted to the false floor and supported my mast step. My plan is to replace the step and 2x4 when I replace the floor, but given what I found under the false floor I'm not sure how I should support the mast step from underneath.

Below the mast step and the false floor I discovered that the 2x4 to which the mast step had been bolted was itself simply screwed to a scrap 2x4 perpendicular to the mast step 2x4. It's weird I know, but this bottom "anchor" 2x4 was not glued or mounted to anything but was just hanging there under the false floor with the mast step and supporting structure above screwed into it.

Also, my mast is actually bolted to an aluminum tabernacle above the deck, so when I refer to the "mast step", I'm actually referring to the base of the tabernacle below deck.

My current rebuild plan is to build a firm foundation of resin covered wood leading up from the hull and filleted and tabbed to the hull. On top of this I'll bolt the new false floor and the 2x4 for the mast step/tabernacle base.

QUESTION#1
Does that free-hanging chunk of wood perpendicular to the mast step serve a purpose in distributing any force coming down onto the mast step?

QUESTION#2
Am I asking for trouble by glassing the lowest portion of my mast support structure to the interior of the hull?

Given that the mast has three stay and is relatively small, am I going to get enough stress that far down in the chain to crack the hull, etc., or will it be well-dispersed by the time reaches the hull?

QUESTION#3
And if these stresses are well diffused by that point, am I just grossly over engineering things by building a monster base glassed in place for the mast step?

Could I get away with a 2x12 bolted and glassed to the frames directly fore and aft of the location for the mast step? To this I would bolt the new false floor and supporting 2x4 for the base of the mast step/tabernacle? This would be less bulky and not directly glassed to the hull?

Is there a better option?

I know the stays sometimes take a good deal of stress, but how much force is exerted on the mast step?



Thanks for your help.

-Glenn

[Roger]

send me an e-mail at roger02 ATT mts dott net and I will show you a picture of how the pvc pipe was used as a mast step support in my DS II as original equipment. Wedging in a piece of pipe, and glassing it in should be suffiecient.

[algonquin]

It appears that your DS has been modified over the years. In this particular case it would be helpful if you could post a pic or two showing exactly what you are dealing with. Do you still have the “mast jack” that the mast rests on ? Brad

[glennk]

Brad,

I'm not sure what you mean by "mast jack", but you can see a pic. of the tabernacle base and supporting 2x4 at this site:

http://glennkaufmann.com/maststep.html

This shows the tabernacle base and support. Below this is the 3/4" plywood false floor, and below that is a scrap 2x4 screwed perpendicular to the 2x4 in the photo (but not glued or screwed to anything but the subfloor. It's basically just hanging there.

My question is, does that "loose"2x4 serve any purpose in diffusing downward force from the mast step?

Thanks.

-Glenn

[Bob Damon]

Glenn, The photo you show is unlike any other O'day Day Sailer, either I, II, or III I have seen. Can you show a full picture of the boat? Thanks, Bob Damon

[glennk]

Bob,

When I purchased it, the boat had undergone extensive modifications from the previous owner, so many of the standard items are a bit off.

That's the reason my questions are less about rebuilding to class specs, than general concepts (how much downward force is exerted on the mast/tabernacle step, and will glassing the base of the step to the hull compromise the hull, etc.)

I've uploaded a couple more pics. at the same site.

The link is:

http://glennkaufmann.com/maststep.html

Thanks.

-Glenn

[GreenLake]

Intriguing situation. Some thoughts:

QUESTION#1
Does that free-hanging chunk of wood perpendicular to the mast step serve a purpose in distributing any force coming down onto the mast step?

I would assume so. I would also assume that some stress was taken up by your 3/4" plywood false floor. The fact that the piece was loose was probably not an issue, since it would have been compressed against the hull under load (if I understand your configuration).

QUESTION#2
Am I asking for trouble by glassing the lowest portion of my mast support structure to the interior of the hull?

If you glass in any wood, make sure that it is really well sealed, so it can't ever wick any moisture and rot. For anything in the bilge, I would be more comfortable with a design where the glass is designed to carry the load, by forming a thick walled channel around something unaffected by moisture like a small block of foam.

Given that the mast has three stays and is relatively small, am I going to get enough stress that far down in the chain to crack the hull, etc., or will it be well-dispersed by the time reaches the hull?

You could estimate the forces, if you like. Stays are usually tightened to somewhere in the are of 5-10% of breaking strength. The latter you can look up online somewhere. Multiply that by 3 (for the three stays, ignoring the non-downward component of the pull) and you get a rough estimate of upper range of the forces involved.

(One of ?) the standard design(s) to support the mast is a glassed inverted square U channel that runs fore and aft. On my boat it appears hollow, but it could have had wood in it at one time. (It's open at one end, but I can't look inside). The mast jack for the keelstepped mast is simply bolted to that channel.

Apparently that's enough to distribute the force.

The hull at that point still has a bit of a V, which is a rather stiff shape in and of itself, and likely to withstand quite a bit of force w/o bending in the fore-to-aft direction. (There's nothing in the original design to distribute the force, or brace the maststep in a crosswise direction).

[algonquin]

Your set up is far from a normal DS but is similar to many boats that use a mast step on the cuddy. You really don't have a tabernacle. You have a mast step and a compression post that carries the mast tension and weight from the cuddy roof to the base of the hull. Most DS’s have a mast jack that the mast rests on and you literally jack the mast upward to tension the bow and side stays. Your boat doesn’t have this feature. Your boat probably has adjustable turnbuckles on each stay that allow you to tighten/adjust the stays.

Basically, I would encapsulate the support that you already have at the bottom of the hull in fiberglass. It is beefy enough as is. No need to get to fancy or overbuild to extremes. The compression post looks quite beefy. I had a 25 foot sailboat that used a 3 x 3 compression post. I would fasten the compression post to that bottom support (use commercial type angle brackets) and make sure that the compression post fits snugly between the bottom support and the inside cuddy roof. When you step next to the mast step on the cuddy roof you shouldn’t be able to feel any give in the roof itself. Your weight should be supported by the compression post. Brad