Mast repair

[bins73]

Hi. I’m after some advice please. I have a solid, Douglas mast of around 17’, with a constant diameter of 4”. Approximately 5’ from the top is an area of rotten timber, associated with screws which held the hounds on, just below the point where the shrouds were secured with loops around the mast.

I have routed out the wet wood, and was planning on scarfing and epoxying in a replacement piece.

My question is, will this repair be likely to return the mast to its original strength (assuming that the wet wood has been giving no structural strength for the last few seasons), or is the depth of the repair sufficient to write the mast off - would I be better to simply replace the mast? Is the lateral force on the mast, just below the shroud attachment significant (I assume it’s balanced by the contralateral shroud), and therefore is this an area of the mast that is even more critical?

I’ve attached some photos of the hound seating, the rotten wood as it was, and the area after removal of the bad wood. There is a bit more to remove below the defect (pencil mark), which in hoping will be part of the tapered shoulder of the scarf.

The depth of the defect is about 1&3/16th”

I’d be grateful for any thoughts as you might have.

Thanks

Sam

 

[IanCC]

A repair, as described, would be highly satisfactory imho.

https://www.westsystem.com/app/uploads/2022/10/0617-Wooden-Boat-Manual.pdf

 

[veshengro]

A repair, as described, would be highly satisfactory imho.

https://www.westsystem.com/app/uploads/2022/10/0617-Wooden-Boat-Manual.pdI agreef

I agree, with all the rot removed and a new piece of timber scarfed and bonded in place as stated, the mast will be fine. Equalise the rigging tensions and I'm sure the mast will last for many years.
I once owned a Lysander that had two such well executed repairs to the mast ( Not by me) and never had any problems.

 

[DownWest]

Sounds good. Scarfs should be 12:1 on masts. Personally, I would remove the step and scarf in a single piece of wood. It is a bit complicted by the luff groove, but there are ball routers bits that can sort that. Maybe put a bit of soft rubber tube to keep the glue out of the groove.

 

[bins73]

Thank you all, that’s reassured me and I’m looking forward to the job - off to the sawmill tomorrow to get some Douglas. I think I agree with DownWest, and will remove the step, which should make it a simpler job, and will also mean the shrouds compress the scarf.

I’ve been reading Bud McIntosh’s book on building a wooden boat, who covers this sort of thing pretty well as well.

In fact the groove is for internal cabling to the masthead, rather than the luff, so I can ignore it and re-rout it once the scarf is in.

I’ll put some photos up as the repair goes along.

 

[AntarcticPilot]

I agree, with all the rot removed and a new piece of timber scarfed and bonded in place as stated, the mast will be fine. Equalise the rigging tensions and I'm sure the mast will last for many years.
I once owned a Lysander that had two such well executed repairs to the mast ( Not by me) and never had any problems.

I think the crucial phrase above is "with all the rot removed" Rot is a fungal infection, and the fungal hyphae might spread well beyond the visible rot. So I would go beyond the obvious rot when removing the damaged wood, and treat the cut surfaces with an anti-fungal agent.

 

[westernman]

Done properly the repair will restore the mast at least to its former strength.
The scarf needs to be long enough.

 

[Daydream believer]

If you are worried about the hounds slipping down the mast due to shroud tension you could fit 2 or 3 small "knees" on the face of the mast tight under the hounds strap. These would be glued & screwed to the mast & neatly shaped in a tapered form. It would assist the load of the screws in the hounds.

 

[bins73]

Thank you for all the advice. I ended up making a jig and routing out a fair bit more, mostly in order to make sure the shoulders were square with each other. Then made the scarf and bonded it with Cascophen. Fairing it today. I’d be grateful for any thoughts about the likely strength of this fix, in particular as the grain density is quite different in the repair when compared with the mast. The repair is Douglas fir, which I’m pretty sure is what the mast is as well.

 

[winch2]

Nice workmanship. Ive just refinished our old mast which had some minor decay here and there, and the biggest thing I reckon is that the spar needs to be completely dried out before doing anything.... removing all the old finish then leaving it for an extended period in a draughty dry environment. I was actually amazed by the difference in weight after leaving the mast inside an old boat shed for three months.

And yes, fungus and rot love any timber thats not bone dry so if you've done the work and then finished it without it being so....you may have further probs.

To beef up our hounds so to speak we fitted a small stainless band underneath.. looks pretty neat and is very secure.

 

[DownWest]

Looks good, quite difficult to get the close joints that Cascophen requires, esp in that curve.