Visit our Popular Forums

champo · 17-02-2019, 23:06

Hi All,

I'm planning on joining my dodger and bimini together to provide more protection and external living space. To do so I will have to relocate the mainsheet traveler as its located between the two covers. My boat is solid Adams 40 and there is more that enough room to install the new traveler forward of the dogger and run sheets etc.. back to the cockpit.

What I'm trying to figure out is what strengthening, if any, would need to provide to the deck area which would house the traveler? I believe the deck is about 8mm thick, there is zero movement when i walk on it and I'm 100kg. I was planning on removing the cabin headlining and installing a 4mm sheet of aluminium which would measure approx 1300mm x 300mm and attach the new traveler by drilling down through the deck into the aluminium sheet and bolting on to the sheet. Would this be OK? Any other ideas? Has anyone done this before?

Thanks Tim.

psk125 · 18-02-2019, 07:46

People have done this before. When they don't do it right, sometimes the traveler rips off the cabin top, or the entire cabin. Your walking on it is NOT equivalent to the forces involved with a main traveler. 100kg? The mainsail on a 40' boat likely has a load more like 1000kg (there are formulae for figuring this out) and the pull is UP, not down. Besides reinforcing the cabin top with your aluminum sheet(and perhaps additional layers of fiberglass or other support) the cabin trunk may also need reinforcement, perhaps by installing knees, to keep the whole thing from getting pulled sideways. Then you will need to look at your boom. The sheet probably goes to the end of the boom now. Moving the sheet to mid-boom gives you less of a lever arm so you will likely need more mechanical advantage to trim the sail. This means you'll need a longer sheet and/or perhaps a winch (which is a slow way to make adjustments). Putting the sheet mid-boom can also make the boom bend or break there. Mid-boom sheets typically go through three sets of blocks on the boom, spread out so as not to concentrate the load too much in one place. Your boom may need reinforcing or replacement in order to take this load. It would probably be a good idea to discuss this change with a naval architect or engineer. There seem to be a wide range of different Adams 40's of of different materials and designs. The solutions will be just as wide-ranging.

Cheechako · 18-02-2019, 07:59

Many boats are built that way. I have not found anything additional added when they do on the ones I've had. Assuming your deck is glass/core/glass, a good backing plate ought to handle it. If you want to be really careful then remove the core in the areas where the bolts go through and put in solid wood or ply then the backing plate.Make sure your boom is adequate for the mainsheet attachment being further forward though.

"sometimes the traveler rips off the cabin top, or the entire cabin" I have not seen that in 50 years of boating.

Think of it this way, the number of bolts holding the traveler to the deck far out weighs the few smaller, or single bolt that holds the bail onto the boom! A traveler probably has a dozen 5/16-3/8 bolts. The boom probably has one 3/8" bolt or a few small ones.

psk125 · 18-02-2019, 10:03

Quote:

Originally Posted by Cheechako

Many boats are built that way. I have not found anything additional added when they do on the ones I've had.
Think of it this way, the number of bolts holding the traveler to the deck far out weighs the few smaller, or single bolt that holds the bail onto the boom! A traveler probably has a dozen 5/16-3/8 bolts. The boom probably has one 3/8" bolt or a few small ones.

Boats that are built for mid boom sheeting with travelers on the cabin top ARE built that way. The forces involved have been calculated and the cabin sides and top designed and constructed to handle it in the first place. Sometimes the travelers are built on arches to solve the problem. Moving things around without planning and being sure could be a big mistake. The OP seems to have an Adams 40 (?) When you google it, the boats that come up vary from racing sloops with bendy spars and running backstays, to hefty fiberglass cruisers, to heavy steel boats with solid dodgers. The OP has not posted a picture, so it is best to err on the side of caution. He also says he wants to move the traveler to the cabin top forward of the dodger, which is not the same as perhaps mounting it to the deck.

Thinking of it as lots of bolts holding the traveler to the deck vs one bolt holding the bail on the boom is exactly why sheeting arrangements have to be thought out as well. All the pressure focused on one bail now in the middle of the boom can cause it to break there. That might happen before the cabin gets pulled apart, which would be a good thing. The forces involved are considerable. Imagine that the boom is 5 meters long. Say the sail pulls up with 500 kg of force at the end where the sheet is now. If you move the sheet 2.5meters forward instead of attaching it at the end, that same 500kg of force is doubled to 1000kg because you have halved the length of the lever arm that the sheet takes advantage of. To carry it further, imagine trying to control the mainsail with a sheet attached just .5m from the mast. You would need a huge mechanical advantage and incredibly strong spars and fittings to do this. That is why sheets get placed at the end of the boom instead. Physics. The OP's idea may be sufficient, but it makes sense to be more aware of what's involved and be sure before starting to drill holes.

champo · 18-02-2019, 16:09

Thanks for the feedback guys. It's never as simple as you'd hope and the last thing I want is a convertible 40 foot yacht so I'll try to locate a marine engineer as a starting point.

**Jim Cate** · 18-02-2019, 18:25

Quote:

Originally Posted by champo

Thanks for the feedback guys. It's never as simple as you'd hope and the last thing I want is a convertible 40 foot yacht so I'll try to locate a marine engineer as a starting point.

Adams 40s have been built by a number of individuals/firms. Do you know who built yours? If so, they will know more about the scantlings than some random engineer. From what you've told us, sounds like a glass build rather than steel, cold mold or alloy construction. As mentioned above, knowing how the house was laid up is pretty crucial to the analysis, so if the builder isn't accessible, perhaps some test holes drilled in the deck would give some useful info.

I'd try to gain this data before contacting an engineer, for without it, he'd be guessing just like we are!

Jim

champo · 18-02-2019, 19:21

Hi Jim, thanks for your input, very wise. I've attached a few pictures which show the boat, the current location of the traveler and where it's to be located if moved.

The boat was built by a well know (at the time) shipwrights the Trewatha Brothers in Victoria but I've had no luck locating or contacting them but will keep trying. I'll do another post to see if anyone has updated info on them.

I'd be interested in any other comments you (or others) might after viewing the pics but I think a core drill is probably a good place to start,

Thanks Tim.

Tillsbury · 18-02-2019, 19:31

One word: Platino. NZ$4m spent on a rebuild including moving the traveller. Didn't work out well. Do not ever underestimate the sizes of the forces involved here.

https://slowboatsailing.wordpress.co...g-nz-yachting/

psk125 · 18-02-2019, 19:48

yikes! They moved the sheet & traveler forward from the original end of the boom design in a "no expense spared" refit. It tore apart in a gybe in a 30 knot wind, immediately killing one crew member and knocking another overboard (not recovered). The uncontrolled boom ended up bringing down the mast. Guess the cabin top stayed on. Small comfort.
https://www.maritimenz.govt.nz/comme...eport-2016.pdf

Champo's photos show the bendy-mast boat with running backstays - built light for heavy-duty racing activity. The boom extrusion is likely as thin as they could make it. Changing to mid-boom sheeting will probably require a much stronger new boom or hefty sleeving in the way of the sheet. Looks like a nice boat!

champo · 18-02-2019, 19:55

Must of been a terrifying few moments, will tread carefully.

nwdiver · 18-02-2019, 20:06

Take a hard look at the boom also, you will be moving the main sheet from the end to a point forward I think this will have to be considered, you may need a new boom......

Cheechako · 19-02-2019, 08:00

Many travelers seem to just bridge over the sliding hatch weather cover. Using the 3 attachment type of bail on the boom like in pic 1 and 4 is a good idea to distribute the load.