Rotten spot in boom.

The boom on my Marine Trader 40' sedan has a soft ie rotten spot. It is half way along the boom, on the bottom half, about 18" long and goes into the boom thickness about half way in about 1/4 of the rotten area and is 2" wide at it's widest. The boom is completely dry. Options, 1. Impregnate the area with epoxy, the boom is made of mahogany, 2. Build a new one of treated wood or build one of aluminum. Ok, what say you gang,. Thanks, J.T.Duncan.

Can you find a local carpenter to scarf in another piece of Mahogany?

What do you use the boom for?

I think my question is key.

My advice, for what it's worth will be based on your answer.

I just replaced my mast and boom on my DeFever.

Mike

I didn't think of a scarf, good idea.
I use the boom to hoist a dingy that weighs about 250 pounds. What did you replace your mast and boom with?

Mine is aluminum but if what you have is lifting the dink even in it's current condition then why not just inject with Git Rot penetrating epoxy which can only add to the strength? There can always be plan B if the cheap way out doesn't work out.

Scarf...if it's painted...doesn't even need to be pretty if you are a good sander and use thickened epoxy. Any hardwood would be fine..if gluing to teak...make sure yu follow standard teak gluing recommendations and I would add a few mechanical fasteners too.

Rot will return. Aluminum may need repainting in a few years. No contest.

A scarf is called a Dutchman, and would be the normal repair.

In early days the woodwork would have to be good , but today as noted Epoxy will allow crap work to be as strong as wood art.

The loads on a boom are mostly compression , most is quite strong in compression , so the Dutchman is mostly just there to keep the boom straight.

You may get by with a Dutchman but in the document you will find here: http://www.pacificmotorboat.com/downloads/Wooden_Hull_Guide_nvic7-95.pdf
is a lot of good reading on wood boat repairs. There are sections dealing with nearly every aspect of wood inspection and types of repairs based on the chosen objective.

In my view a Dutchman would be used to make a cosmetic repair. A properly executed scarf would be a better repair on your boom and wood (pun intended) return it to its original strength without a huge increase in your work load. Either way you have to cut, glue and refinish so why not do just a little more for the better fix?

If you are more comfortable cutting drilling, riveting and/or screwing find a piece of aluminum to use. Although, unlike wood eventually the aluminum will corrode and you can't put a scarf in it

Having had a dinghy drop suddenly because of a failed shackle, I would be very careful about how this boom is repaired/replaced. Even though you have a relatively light dinghy/motor combo, you or the next owner may get a heavier set-up. Our RIB/motor weighs about 650lb!! Another factor to consider is the significant additional strain on the boom lift when there is wake or wind while lifting the dinghy. The swinging motion can exert a significant additional strain.
If it were me I would replace either with new wood or aluminum. I do not believe a scarf joint is intended for load bearing. A possible option might be to sleeve the affected section with ample overlap on both sides of the bad section with aluminum pipe.

epoxy will not fix it.

pauloman said:

epoxy will not fix it.

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Or to clarify, epoxy alone will not fix it. Replacing the boom with aluminum tube is fine but new fittings will have to be made or acquired, including a new gooseneck and mast mount for that....causing more trouble than it's worth in my view.

An aluminum tube (probably sch 40 aluminum pipe) is just that, a straight tube, whereas a wooden boom can be shaped and tapered. Important to some, of no consequence to others. Better to repair the wooden boom properly.

Take the boom off the boat, cut away the rotten part, then cut away some of what appears to be sound wood around the rotten section. Make the bottom (parallel to the length of the boom) of the hole flat and the ends of the new part sloped in 8/1 to 12/1 scarfs. If the new piece is thicker (deeper) than 3/4" laminate two layers of new mahogany in the hole. Best is leave it rough shaped when you glue it in, then finish shape and sand to match the existing wood. If properly executed this repair will as strong as the boom was when new (all wood has some flaws), the boom will also be stiffer (less bendy) than it was when new.

I put a two foot Douglas fir extension on a 3 1/2" teak boom. I used West System on the project, but put stainless straps on both sides just to be sure. Just throwing out ideas. My dingy and motor are only 165 lbs. I would be cautious of heavier loads.

Chrisjs said:

A possible option might be to sleeve the affected section with ample overlap on both sides of the bad section with aluminum pipe.

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A repair or extension to a sailboat mast often involves a sleeve. A good repair plus some form of reinforcing sleeve should do the job, it has to be stronger than the rotted section which I gather was discovered without failure having occurred.

Fridaze, very nice job. With that sliding lift sailtrack system on the bottom of the boom, you're clearly putting different loads on the boom than the normal compression loads you'd expect if the rig was designed to lift only from the boom end, and the stainless straps are probably more than just "belt and suspenders.

Well ARoss "the truth be told" after I put the traveler on the boom and did the first test I decided I didn't need it. The boom length was enough that I could raise it 30 degrees and still clear the rails with the dingy. The 30 degrees centered the hook over the lift cables. So, the boom stays in compression and I believe I have plenty of margin on the rig for my less than 200 lb lift. I wasted a bunch of cash on the sailboat gear that is now abandoned in place.

thank you one and all for your comments. I have decided to build a new boom out of wood. I am leaning towards Ash as the perferred material.

My understanding is that Sitka Spruce is by far the preferred wood. Second best is still Spruce. Not sure why you would select Ash??

Tad Roberts said:

Or to clarify, epoxy alone will not fix it. Replacing the boom with aluminum tube is fine but new fittings will have to be made or acquired, including a new gooseneck and mast mount for that....causing more trouble than it's worth in my view.

An aluminum tube (probably sch 40 aluminum pipe) is just that, a straight tube, whereas a wooden boom can be shaped and tapered. Important to some, of no consequence to others. Better to repair the wooden boom properly.

Take the boom off the boat, cut away the rotten part, then cut away some of what appears to be sound wood around the rotten section. Make the bottom (parallel to the length of the boom) of the hole flat and the ends of the new part sloped in 8/1 to 12/1 scarfs. If the new piece is thicker (deeper) than 3/4" laminate two layers of new mahogany in the hole. Best is leave it rough shaped when you glue it in, then finish shape and sand to match the existing wood. If properly executed this repair will as strong as the boom was when new (all wood has some flaws), the boom will also be stiffer (less bendy) than it was when new.

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Tad gives you a thorough answer to your question. And the right answer. Use the same wood as original.

I lengthened a box mast on a Choey Lee Sailboat for a friend using only scarf joints and good glue. I built a solid tapered mast for my Bolger Black Skimmer skimmer of store-bought fir that needed two lengths scarfed together for the total length. Worked like a charm.

Good prep and good glue is all you need. If your joints are perfect, Elmer's will actually work OK.

Adding metal reinforcements only adds to early failure and potential for more rot. Coating the rot with epoxy won't work either.

awpptdt said:

thank you one and all for your comments. I have decided to build a new boom out of wood. I am leaning towards Ash as the perferred material.

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Forget ash. Fir or white pine will work better. Spruce, too with modern epocy coatings you don't need traditional boat building wood just spend some time at Home Depot picking some good pieces You can either laminate several boards or buy a nicely grained single piece and hope as necessary.

Use whatever wood meets the reasonable test...here's a quickie source of info from a reputable company

Boat building lumber and plywood 4.