Running mainsheet inside boom

Gonzo

You might be on to something. The client is very touchy about aesthetics. Rightly so, this will be a beautiful boat when finished. A pipe won't cut it, but perhaps an aluminum envelope of some kind welded to the outside. That would get rid of the notch on the boom.

RHough

You are asking questions that don't apply to this thread. Please re-read my original post.


edit:

Gonzo, I see you said 'half pipe'. That's the ticket!

 

I did read the original post. That's why I asked the questions.

Excuse me for seeing issues that have not been addressed.

R

 

I Guess the customer is always correct and your job is to figure out how to do it, but from a sailors point...its a bad deck layout idea.

I would use a classic two to one mainsheet system, led aft and powered by two fast electro hydraulic winches. Its critical that the helmsman can operate the mainsheet and its critical the the sheet system is very fast to control the main in the jibe.

If your boom and vang is strong enough there is no need for a traveler. Most modern yachts have done away with travellers. By eliminating the traveller you will make your mainsheet system even simpler , faster and clean up the cockpit of travellor control lines. Are you familiar with the Cariboni system ?

http://www.cariboni-italy.it/public/caritec/products/datasheets/magictrim.pdf .

If It were me I would rig the boom with an internally run a main boom preventer to triangulate the mainsheet against the boom topping lift to stabilize the boom for sailing in a seaway . This main boom preventer shall be led forward then aft to the steering cockpit

What is the purpose of a boom gallows ? It is difficult to seat the boom in a seaway...you will always damage the paint. Gallows make it impossible to compress the vang, lower the boom and work on the outboard end of the boom when stripping the main. The gallows also interferes with center cockpit dodger design.

 

This should be fairly straightforward.

Assuming you are bringing the mainsheet into the boom from a slot in the bottom you would want to build a roller cage to reduce friction/chafe where the sheet enters the slot when the boom is let out. This is normally done for spinnaket halyards on bigger boats, so your sparmaker should have some idea of how to accomplish this.

The slot in the boom would only have to be as wide as the sheet, plus clearance. It would only have to be long enough to allow a fair lead from "on CL" up to the maximum angle the boom will ever be let out. That should be easy for you to model. Of course the cage can help reinforce the area, and you could add a sleeve if someone is concerned about any weakness in the area due to the material removal.

Inside the boom you would have a hanging block that would have to articulate to compensate for the change of angle as the boom is let out and/or the change of sheet angle from tack-to-tack.

The sheet would exit to a block directly under the gooseneck.


Of course this is assuming the mainsheet is single ended and would only go to one of the winches in the cockpit. If you wanted to double end the sheet to both winches (similar to the "German Style AC mainsheet system") that would make things quite a bit more interesting.

 

Thanks Paul. This is exactly the sort of thinking I was hoping for.

The sheet is double-ended. The hanging block is what I have modeled in the end of the boom (in the bottom image). The designer's concern in this area has to do with the loading on the leach. But, if we did something as Gonzo suggested, we would not have to reduce any cross section.

I think what I will propose is a half-pipe with some sort of fairlead into each end. In fact, it could just be a section that's only a few feet long.

As for Michael's question about 'why have a boom gallows'?

I'll ask why was the Maltese Falcon built as a 'square rigger'?

These are just a couple of the thousands of questions asked that have the same answer: "Because!"

 

For a double ended sheet I think you would run out of room at the gooseneck area for the blocks. You might need to exit them through slots on the sides of the boom to get nice, fair leads. You would also have to have two entry slots spaced apart by a little bit on the bottom of the boom to make sure you didn't run out of room inside the boom at the sheet entry.

In my description the hanging block is inside the boom.


I have no idea what your designer means about loading on the leach. If your mainsheet is near the end of the boom and the leach is near the end of the boom that sounds pretty good to me.


FYI, in the post preceeding mine there is a picture of a boom with just the type of roller cage I was describing. It is where the red line enters the boom. Take a look.

 

The AC system works fine but its clumsy on a cruising boat...lines everywhere.

Also remember that the design is spec'd for a roller boom. Not much space inside and on the front end of a roller boom. This space is needed for a dedicated main boom preventer and a dedicated storm trysail downhaul tack fitting.

Also consider that the mainsheet loading will be transferred to the gooseneck then cabinhouse. Very clumsy....best to concetratre the loads on the main travellor bridge deck then run the sheet to the helmsman with the shortest possible sheet, least friction and least amount of sheet coiled up in the cockpit.

The yacht pictured will have..mainsheet, mizzen sheet, genoa sheet, staysail sheet, Spinnaker sheets, traveler lines and preventer all in the steering cockpit...thats a mountain of spaghetti.

Are you laying out a 4 winch or 6 winch helmsman's cockpit? How will you run the staysail sheets aft to the cockpit ? Staysails are narrow sheeting angle sails, inboard track, and must be run aft along the cabin top. Running the staysail sheet inside the hollow ss cabintop handrails works on many boats.

 

As I understand it the CC winches or lead aft is an either/or not a both at the same time?

The CC winches used while racing or when extra crew available? The aft lead for cruising or short handed? Will the main vang always run aft or will it need a CC lead also?

The side view shows the main sheet running forward to a block on the deck, then outside the Dorade box past the CC combing then aft? Does this repeat on the port side so the sheet is trimmed from both sides of the aft cockpit also? That is a huge amount of line to deal with and added deck clutter that is not needed.

For the aft lead dead end the port side of the sheet, lead the starboard side back to the aft cockpit. When the CC winches will be used you simply run the sheet through the turning block the other way and lead it forward to the CC winches. Less line, less chafe on deck, no need to lead past Dorade box etc. etc.

I've taken the liberty of adding to the images you posted. The mainsheet as you have in the side view is drawn in red on both. The dark green is the aft lead, the light green is the forward lead.

Leading the mainsheet forward, through the boom than back on deck to the aft cockpit will add an unbelievable amount of friction. The line will get walked on and chafe everything along its length. Shorter and fewer turns in blocks would be better. I don't see the deck hardware in place on the 3D rendering, fair leads look to be a problem to reach the aft cockpit if you go to the mast then back.