Relocating the main sheet traveler

[Wind River]

I have a Hudson Force 50 Center Cockpit ketch.

I want to relocate the main sheet and traveler from behind the helm seat inside the cockpit to the cabin top in front of the cockpit to clear the access in and out of the cockpit. I have seen this done on similar boats but they all had aluminum booms. Mine is a box constructed wood boom that is 5.25" x 4.5" at its widest point.

My boom is 20 feet long and the sail foot is about 19 feet. The new attaching point would be about 9 feet out from the mast so there would be a little more than half the boom unsupported. There is less sail area over this portion, but would that really help the situation?

I realize I will need to increase the purchase on the main sheet to compensate for the lost leverage and the cabin top would have to be reinforced to take the load. That aside, is a wood boom (in good condition) up to the task of being sheeted from less that half its length?

I can fabricate a mount for the sheet attachment that clamps around the boom instead of a penetrating it at its point of leverage/load if that helps.

Thoughts?

[UNCIVILIZED]

It's an educated guess, but I'd say No, not a good idea. As you'll be doubling the loads on; the boom, the sheet's attachment to the boom, the blocks, the line used for the sheet, the traveler + it's car, & the structure that the traveler is bolted to. Which, any, or all could/would be subject to self destruction at some point.
Harken has a sheet load calculator if you want to run the numbers.

Also, you'd likely be better off using either a soft, "saddle" type connector, for attaching the sheet blocks to the boom. Basically a very wide fabric, & webbing strap, with D-rings at each end, that encircles 300 degrees of the boom's circumference.

And to go one better, use multiple attachment points for the blocks, spread out over a fair span length on the boom. So that if you have 5 sheaves total, in blocks on the boom. Then ideally you'd go to 5 individual blocks attached to it, each one attached with webbing, or a spectra strop. Thus no point loading. Though even with this kind of setup, you're doubling the loads on all of the sheet's components if you move it that far forwards.

If it's really important to you to move the sheet out of the cockpit like that, have someone run the numbers for you on how strong a boom you'd require in order to handle the increased loads. And then go shopping for one, along with some new blocks & deck hardware. Which, all of the above components are fairly easy to find used, in good condition, cheap.

Though you might also have to build a beam on, or under the deck, tied into some major structural members, to handle the traveler/sheet loads. Be it wood, wood/carbon or wood/composite, or aluminum. Assuming that is, that the coach house can handle such loads in the desired location. So if there's a bulkhead near to where the new traveler would be mounted, that would help immensely. But it to could require some beefing up, in terms of how it's tied into the deck & traveler, plus coach house sides.

And the new "boom" can even be a segment of mast section liberated from disuse somewhere. Just plan on adding all of the proper end fittings, & internals:
Reefing lines, sheaves, & stoppers for same
Outhaul
Gooseneck
Vang attachment point, with boom doubler
And the rest of them can be attached via spectra strops. Like the sheet blocks, preventers, etc.

However, you might get away with strengthening & stiffening the current boom via adding some carbon, or E-glass unidirectionals & Triax. Or a lot of extra wood. That or some structural wings added on, made from aluminum, stainless, wood, or composite. You could convert it to the Park Avenue style too, that would give you the needed strength & stiffness.

[Wind River]

Originally Posted by UNCIVILIZED

It's an educated guess, but I'd say No, not a good idea. As you'll be doubling the loads on; the boom, the sheet's attachment to the boom, the blocks, the line used for the sheet, the traveler + it's car, & the structure that the traveler is bolted to. Which, any, or all could/would be subject to self destruction at some point.
Harken has a sheet load calculator if you want to run the numbers.

Also, you'd likely be better off using either a soft, "saddle" type connector, for attaching the sheet blocks to the boom. Basically a very wide fabric, & webbing strap, with D-rings at each end, that encircles 300 degrees of the boom's circumference.

And to go one better, use multiple attachment points for the blocks, spread out over a fair span length on the boom. So that if you have 5 sheaves total, in blocks on the boom. Then ideally you'd go to 5 individual blocks attached to it, each one attached with webbing, or a spectra strop. Thus no point loading. Though even with this kind of setup, you're doubling the loads on all of the sheet's components if you move it that far forwards.

If it's really important to you to move the sheet out of the cockpit like that, have someone run the numbers for you on how strong a boom you'd require in order to handle the increased loads. And then go shopping for one, along with some new blocks & deck hardware. Which, all of the above components are fairly easy to find used, in good condition, cheap.

Though you might also have to build a beam on, or under the deck, tied into some major structural members, to handle the traveler/sheet loads. Be it wood, wood/carbon or wood/composite, or aluminum. Assuming that is, that the coach house can handle such loads in the desired location. So if there's a bulkhead near to where the new traveler would be mounted, that would help immensely. But it to could require some beefing up, in terms of how it's tied into the deck & traveler, plus coach house sides.

And the new "boom" can even be a segment of mast section liberated from disuse somewhere. Just plan on adding all of the proper end fittings, & internals:
Reefing lines, sheaves, & stoppers for same
Outhaul
Gooseneck
Vang attachment point, with boom doubler
And the rest of them can be attached via spectra strops. Like the sheet blocks, preventers, etc.

However, you might get away with strengthening & stiffening the current boom via adding some carbon, or E-glass unidirectionals & Triax. Or a lot of extra wood. That or some structural wings added on, made from aluminum, stainless, wood, or composite. You could convert it to the Park Avenue style too, that would give you the needed strength & stiffness.

Where would I find someone that can do this?

So is my gut feeling right to think that a box wood boom is not as strong as an aluminum one? I really don't want to go mixing materials if I don't have to but I would really like to move this traveler out of the cockpit.

I have plans to build a hard top for this boat. I could raise the boom about 12" and put the traveler on the top of the hard top like the boat in this picture.
This may be the better option as I plan to raise the mizzen boom up 12" also to allow a bimini under it. Do you think loosing 20 sq.ft. of a 513 sq.ft. main sail will be detrimental to this type of cruising boat?

[Wind River]

This is a traveller on a Formosa 51 Center Cockpit.

It does not look like the mounting of this would hold based on the Harken load calculator even if the cabin top was reinforced. According to the calculator, this mounting will have almost 8000 lbs of sheet load at 30 kts. 14,000 lbs if caught un-reefed at 40 kts.

[UNCIVILIZED]

Originally Posted by Wind River

Where would I find someone that can do this?
I would think that any competent rigger could. They'd first need to approximate the current boom's section modulus (strength, & stiffness), & then multiply it by the appropriate factor(s).

So is my gut feeling right to think that a box wood boom is not as strong as an aluminum one? I really don't want to go mixing materials if I don't have to but I would really like to move this traveler out of the cockpit.
Strength of the boom is dependent on that of the materials it's made from, how much of them is used to make the boom, as well as the size of it's box section, & it's wall thickness.
So an aluminum one needn't necessarily be stronger, though it'll likely be lighter for the same strength.

I have plans to build a hard top for this boat. I could raise the boom about 12" and put the traveler on the top of the hard top like the boat in this picture.
It's obviously possible, though that's a lot of load for the bimini to carry. Think about the forces involved with a sail that size during an uncontrolled gybe in say 25kts.


The longer the lever arm which a force has to act upon, the larger the loads will be. Whether it's the height of the bimini, or the elevated traveler towers pictured.


Also, sometimes I think that the Harken mainsheet loading formula is kinda' skewed, since if you use the formula to calculate for a jib of the same size. And then double it to take into account mid-boom sheeting, the numbers are half of those generated by the mainsheet calculator.
Then again, jibs don't shockload their sheets or hardware when you have an accidental gybe, like mains are prone to doing.

This may be the better option as I plan to raise the mizzen boom up 12" also to allow a bimini under it. Do you think loosing 20 sq.ft. of a 513 sq.ft. main sail will be detrimental to this type of cruising boat?

You'll lose more sailing ability (efficiency) due to the huge drag from the bimini & it's supports, vs. the 20sqft loss in sail area. Which you can often make up for in other areas anyway.

The pictured structure is about the equivalent of towing a submerged shopping cart 24/7. Due to it's parasitic drag, plus the interference with the air flow over the sails which it creates.

Some designers are now (FINALLY) going to aerodynamically faired arches/solar panel farms. Including the side struts on them. And integrating the panels into smooth, fair structures on top. Which are integral to the entire arch structure. So that the whole unit is one aerodynamic, monocoque piece. That even includes facilities for hoisting & lowering the dink (built in davits), which again are part of the whole aerodynamic structure.
This is a huge benefit to reducing added windage. Plus it's a heck of a lot more pleasing to the eye.

[Wind River]

Originally Posted by UNCIVILIZED

You'll lose more sailing ability (efficiency) due to the huge drag from the bimini & it's supports, vs. the 20sqft loss in sail area. Which you can often make up for in other areas anyway.

The pictured structure is about the equivalent of towing a submerged shopping cart 24/7. Due to it's parasitic drag, plus the interference with the air flow over the sails which it creates.

Some designers are now (FINALLY) going to aerodynamically faired arches/solar panel farms. Including the side struts on them. And integrating the panels into smooth, fair structures on top. Which are integral to the entire arch structure. So that the whole unit is one aerodynamic, monocoque piece. That even includes facilities for hoisting & lowering the dink (built in davits), which again are part of the whole aerodynamic structure.
This is a huge benefit to reducing added windage. Plus it's a heck of a lot more pleasing to the eye.

I understand what you are saying, but on my boat the traveler tower would be inside the enclosed cockpit. I don't see where there would be any more drag than it has now. The aft bimini may add some drag, but look what I am sailing..... I'm not going to win any races with this boat. I want my wife to be comfortable and out of the sun so I can keep on sailing, however slow that may be.

I am prone to overbuilding, but if things like the traveler tower and the cabin top traveler I have shown in pictures, are working for these boats, my designs are sure to be adequate as I would not have settle for those designs.

This picture shows the aft bimini I am looking to duplicate

[Matsubob]

My first concern would be the boom. It would be "out of design" and the newly added forces in the center will cause the boom to bow in the middle without reinforcement, or replacing it altogether. Any amount of tackle can be added to "tame it" but physically the original boom would be the issue.
THEN think about reinforcement of the traveler cage or tracks or whatever.

[foufou]

As was posted in another thread on structural engineering, doubling the depth of a beam (boom) increases the strength by 8. A cubed relationship. So increasing the wood on top of and on the bottom of the boom such that the boom is 30% greater top to bottom might make it strong enough. The wood could be tapered from maximum at the load point to both ends so it doesn't look clunky. Don't take this as a precise calculation but meant to give you a sense of how to look at boom modifications would affect the strength.

[Jim Cate]

I wonder if epoxy and carbon tows or possibly S-glass along top and bottom of the boom would add enough stiffness to make it work? Somewhat easier than increasing the thickness of the flanges to achieve strength, I think. An awful lot depends upon how "overbuilt" the original boom is. There is a lot of variability in such factors in Taiwan built vessels of that era IIRC.

Jim

[nautitrix]

My major concern has been addressed here but I will say it for emphasis. Put three attachment points for sheet blocks on the boom to distribute the
load over the length of the boom.

[Wind River]

Thanks for all the input. I'm still not sure of the approach I will take, but the feedback is appreciated.

I actually feel more comfortable building the traveler arch but I will need to see if I can make it strong enough without taking too much room around the cockpit. I still need plenty of room to work the winches and those will be in the same area the arch needs to mount.

Lots to think about.