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bvv
03-26-2007, 09:16 PM
In a 35 ft sloop, I am considering adding structure in the mast step area to help transfer mast load from the mast step to the shrouds , and am don't know which is better, cast or fabricated bronze pieces. I understand from searching the forum that strength is not appreciably different for either method, and wonder if one is less expensive than the other, or better in some other way.

For the structure, I plan on placing a bronze plate,1/2" thk X 4"W X about 16"L, under the step, and attaching two vertical 'wings' (one each side) to reach out and catch a bronze rod up to the shrouds. Each wing will have one horizontal flange to mechanically fasten the wing to the horizontal plate and a vertical flange at a 90 deg. to lay against and be lagged into the side of the mast step so that the forces will act to compress the width of the step. It is the wings that I will have made.

The reason for the wings, rather than a bent plate, is that I want to move the attachment points of the bronze rods outboard to avoid the cabin sole and conceal the rods in lockers. The structure will be too large to fit under the mast step (between the step and the keel).

Do the 'wings' sound like they'd work?

Thad Van Gilder
03-27-2007, 06:12 AM
wow, your sloop must be way stiffer than my cutter to try that kind of trick successfully!

-Thad

Jay Greer
03-27-2007, 10:45 AM
I usually design a saddle the fits under the mast step. This is then connected to bronze strapping that is connected to a turn buckle on either side by a bronze hinge pin set up. The strapping is attached to the upper shroud chain plate. All is made of strapping or plate and takes up little space.
JG

bvv
03-27-2007, 09:47 PM
Thad,
I'm not sure I know what you mean. Why would the boat need to be stiff to add this structure?

Jay,
That's more or less what I want to do, except that I need to move the attachment point of the strapping to the saddle outboard about 10" each side.

Would the 'wings' be less expensive (or better) cast, or soldered/welded?

Here's a sketch of the project.
http://i10.tinypic.com/454gadw.jpg

Roger Cumming
03-27-2007, 10:32 PM
There are several reasons why this scheme seems ill-advised. (1) The bronze rod when tensioned will introduce a very high bending moment in the wing - in fact the tendency of the wing to bend and deflect upward will prevent the bronze rod from being tensioned anything near to the tension in the shroud. The bronze rod wants to be connected in a straight line to the mast step in order to work properly. But then it would interfere with passage fore and aft next to the mast step.(2) the angle of the bronze rod will induce a high compression force into the deck, much higher than that induced by the chainplates which are more vertical.

The traditional arrangement of chainplates transferring their tensile load into the planking and diagonal strapping helping the planking further distribute this load to a large area of planking works well. The rod connector between shroud and mast step does short circuit the rigging load from the hull but unless you can step over it at the mast step it will be an obstruction.

bvv
03-28-2007, 12:54 AM
Roger,
Thanks for your comments; the conflict between needing passage space for and aft versus the canteliever loading on the wing is the real issue. It sounds like I need to do some calculatons.

One point tho, is that because the rod is more outboard, it is actually more vertical, which seems to me to offer less compression at the deck rather than more.

She does have the traditional chainplates which are fastened to bronze plates, about 18" tall by 4 ft wide , laying over and fastened to 5-6 frames, as well as bronze diagonal bracing from the plates to the keel.

As you point out, any deflection of the wing will defeat the purpose of the assembly. In that regard, the wing would be be 1/2" thk plate by about 4" tall with flanges in the two other planes. I figure the flange next to the mast step will resolve the horizontal forces created by the canteliever loading of the wing upward by pressing against the side of the step. Fastening the flange under the wing to the plate under the step will also help. I could add a plate above or sleeve through the step (similar to the bronze sleeve through the mast at the spreaders) to take the compression load off of the step, if needed.

I should mention that I also intend to place a compression rod vertically from the partner at the deck, then through the step, and to the plate under the step.

Which would be better (cheaper?) for the manufacture of the wing, a weldment or a casting?

Lucky Luke
03-28-2007, 05:29 AM
This looks quite wrong to be, since the tension on your *wing* (it is a half floor, actually) will tend to twist the mast step, and then the keel below or, if it sits on a floor, ask to this floor an effort for which it has not been designed.
A similar and classic arrangement ressembling this one (which has probably inspired your design), is with tie rods from the chainplates to the mast step (as Roger Cummins mentionned), and the whole arrangement has a triangular shape , which is rigid, NOT quadrilateral.
We understand your concern about the passageway, but this would be small price to pay compared to inflicting to this boat efforts that could even open the rabbet.
When doing this sort of (triangular) arrangement, one has to add also an other couple or tie rods, fore and aft of the mast, from the mast step to the beam above, in order to avoid them to bend under the compression they will receive.

George Ray
03-28-2007, 06:31 AM
Assuming it is in the proper location. Can you manage to extend the current bulkhead to be full width/multiple layers and have an oval step-thru access at the passageway. Then use the bulkhead as an attachment point to distribute tension loads.

Thad Van Gilder
03-28-2007, 07:54 AM
I'm just saying that a looser boat will have problems with inducing such tension. Even with a tie rod from the partners to the step, you may get bulging on either side of the mast.

-Thad

Gary E
03-28-2007, 08:00 AM
Would the 'wings' be less expensive (or better) cast, or soldered/welded?


Much faster, less cost, and stronger to fabricate and weld.


What is the purpose of the bronze rod and the turnbuckle?
Describe the forces on it.

alkorn
03-28-2007, 08:15 AM
Why are you using bronze? The problem would be solved if you used a piece of structural steel. You could use a piece of something like 2"x6" channel in a "U" under the mast step. Then weld an eyebolt or a cross-piece with a hole in it at each end. Get the whole thing hot-dip galvanized. Use galvanized or stainless tie rods.

It would be much cheaper and much stronger than bronze. The galvanizing would give out and it would rust eventually, but well-galvanized steel should last a long time.

Dan McCosh
03-28-2007, 08:41 AM
We've used a similar system (with the "wings") sucessfully for years. Some issues, however. You show the wing with a flange on the bottom, rather than the top. This is backwards, as the compression load is on the top of the wing--the bottom is in tension, hence would not tend to buckle.

I can't seem to do visuals, but I'll try to describe our system.

The original mast stem was two 2x6 ins. oak beams, resting on bronze keel floors. A space between the two holds the tendon on the base of the mast.
The reinforcement was adding two stainless plates on the outside of each beam, with a plate welded to the upper edge. This formed two T-shaped beams that were bolted through the original two 2x6 beams. Beneath the mast itself, a couple of 1/2 inch bolts keep the
two plates solidly together, with the original oak step sandwiched between. Two plate "wings" (3/8 ins. stainless) are welded to the flat plates--much as you show--with tie rods leading to a bronze plate that holds the chainplates. The tie rods have a turnbuckle-like adjustment. A bronze arch also reinforces the deck beams at the mast partners, which is tied to the step with a bronze tension rod.

Might note that the mast step itself is reinforced with the steel "T" sections for about six feet fore and aft. The wings are about 18 ins. out on each side. This under a 72 ft. mast that weighs about 800 lbs. It has added considerable rigidity to the mast/ keel.

Jay Greer
03-28-2007, 01:39 PM
The wings will add torque to the support. However, if the assemply is supported by a floor timber, there should not be much cause for concern. Certainly a vertical tie rod up through the center of the deck fwd of the mast will add to the equation. Hanging knees or a partial bulkhead will also help. Lack of this kind of this kind of support is often the cause of leaks as well as the spitting of cotton along the fore foot and garboard rabbet. Welded bronze plate is the material we always use. It can be silver soldered but there can be dissimilar
metal problems generated there.
Jay

Bruce Hooke
03-28-2007, 02:37 PM
Leaving aside the structural and design questions, I agree that fabrication will be cheaper than casting. If there is any economy in casting it comes when you are making many copies of the same part.

donald branscom
03-28-2007, 05:18 PM
In a 35 ft sloop, I am considering adding structure in the mast step area to help transfer mast load from the mast step to the shrouds , and am don't know which is better, cast or fabricated bronze pieces. I understand from searching the forum that strength is not appreciably different for either method, and wonder if one is less expensive than the other, or better in some other way.

For the structure, I plan on placing a bronze plate,1/2" thk X 4"W X about 16"L, under the step, and attaching two vertical 'wings' (one each side) to reach out and catch a bronze rod up to the shrouds. Each wing will have one horizontal flange to mechanically fasten the wing to the horizontal plate and a vertical flange at a 90 deg. to lay against and be lagged into the side of the mast step so that the forces will act to compress the width of the step. It is the wings that I will have made.

The reason for the wings, rather than a bent plate, is that I want to move the attachment points of the bronze rods outboard to avoid the cabin sole and conceal the rods in lockers. The structure will be too large to fit under the mast step (between the step and the keel).

Do the 'wings' sound like they'd work?

Sure wish we could see a photo of the whole mess.
Forget soldering. Welded steel hot dip galvinized, but not WITH BRONZE. That would not be compatable.

Just cannot comment without a photo.
Remember that the frame or frames that a mast step is siting on and the deck beam form a sort of bow and arrow trying to push the mast thru the bottom of the boat. There should be a pin thru the mast at the deck beam to keep the deck beam from flexing up or down.
Steel is about 92,000psi tensile
Bronze (depending on type) can be 380,000psi.tensile
http://i12.tinypic.com/44zy5b7.jpg
http://i12.tinypic.com/44zy5b7.jpg

Roger Cumming
03-28-2007, 08:47 PM
If you were to add a plate across the top of the mast step identical to the bottom plate you would have a much stronger continuous cantilever beam which might help achieve your goal.

The compression in the deck is due to the angle of the bronze rod. As long as the angle remains as drawn, there will be compression in the deck.

I don't understand the "compression" rod between the mast step and the mast partners that you mention. A tie rod at that location serves as a tension member, preventing the deck from deflecting upward due to the deck being compressed by the shrouds. A tie rod will be necessary if you make this alteration. Which brings up the question of why you want to do this in the first place. You are not removing the chainplates and therefore much if not most of the tension load of the shrouds is being distributed to the planking anyway. Unless the chainplates are not doing their job adequately, why add all this rigging? If the chainplates are not adequate they could be replaced with longer ones that engage more of the planking. The rigging loads generated by the mast and shrouds and stays ultimately must be absorbed by the boat's hull structure - its planking, framing and keel. I am not sure your proposed alteration improves the hull's ability to absorb these loads.

Lucky Luke
03-28-2007, 09:21 PM
Assuming it is in the proper location. Can you manage to extend the current bulkhead to be full width/multiple layers and have an oval step-thru access at the passageway. Then use the bulkhead as an attachment point to distribute tension loads.

If the boat is already rigid enough (what type of boat is she???), that could be the best thing to do, the simplest, safest, and cheapest. But it ALL depends on how is the boat constructed.

A question though: do you really need to do all this (whatever it is)? does she leak when heelling, open her seams? Does the hull *work* too much?(can you see the mast moving up-down too much, in a seaway, through the mast hole)? Again: what type of vessel?

As a professional (no pretentious attitude there: there are many *expert- amateurs* right here), I feel extremely reluctant to suggest anything but the proven classics without knowing all the details of the boat and her beheaviour.

Lucky Luke
03-28-2007, 09:25 PM
Donald Branscon:
This is the second time that I see you recommending this *pin* between mast and beams. Unusual feature, and looking potentially dangerous! Do you have references or is it a personal idea?

Dan McCosh
03-28-2007, 09:46 PM
Might add that the alteration to the mast step (on our boat) was originally suggested by Rod Stephens, who had added a similar arrangement to Mustang--another NY32. The reason was basically to distributed the load from mast thrust, reducing the point loading on the keel which had been relatively thin, with the stem scarf close to the step.
I might add that the relatively long step--also reinforced, as noted above--was part of the system. Stephens also noted that the boat had been built with a relatively thin mast step to add to headroom in the front of the cabin, which he saw as a weak point.

A sister ship without this reinforcement has seen the mast step settle about 2 inches. over the years.

Jay Greer
03-28-2007, 09:55 PM
Gentlemen,
With all due respect, I believe the subject has been more than thoroughly covered!
JG