Dent in aluminum mast

I recently bought an Aloha 8.2 sailboat for salvage from an insurance company. Heres the deal,when the owner was standing the mast up last summer the crane operator(marina) disconected the crane and drove away before the owner had the pins in and the mast fell directly sideways landing across the teak handrail on a grand banks. The damage consists of a dent in the side of the mast a few feet below the forestay attatchment point (its a fractional rig) and one side at the bottom being flared out as it came off the mast base (deck stepped mast) I have no intention of replacing the mast,the damage is just not that bad,but i will do any repairs to make it safe.The bottom where it was flared out i have bent back into shape and have cut some pieces from the side of a J35 mast we replaced which match the curvature and am going to sandblast and glue and rivet them on using a toughened epoxy and a layer of veil cloth so i dont squeeze it all out as i cant control the pressure of the ss rivets.
The bigger or maybe smaller issue is the dent in the side, it is barely noticeable as it is more like a 2"x3" depression maybe 3/32" deep in the center, my thoughts are to again epoxy on a splint made out of that J35 mast over the depression and use some 3/16 or 1/4" ss rivets around the center to ensure that it cant go in,i would do the same thing on the other side for symmetry. However my gut tells me i may be able to do nothing so im wondering if there are any actual spar makers ,engineers or naval architects on here who may have a useful opinion.BTW,sleeving from the inside is not feasable and im going to avoid welding as i think it would cause more problems than it would cure.
Thank you ,Steve.

 

SteveW
"...I have no intention of replacing the mast.."
Well, for whatever reason, that is your first mistake.
The mast is a compression post. Once the post has been damaged, in the manner in which you have described, its ability to carry load is seriously compromised.

"..The bottom where it was flared out i have bent back into shape.." in what manner did you do this?..I suspect what ever method you used to achieve this, again will just shortened the life of the mast. Since to straighten requires either mechanical means or thermal means, either are not good for the strength of your mast.

The type of repairs you are doing are like putting a sticking plaster onto a cut to the jugular!...will only hold it for a while.

 

You did already cause more probs than cures! And wasted time and money. Sell it as scrap (it is scrap). As Ad Hoc mentioned, there is nearly no way to get it into service again.
Bad news............. stand it!

Regards
Richard

 

Guys, the boat is a $12- 15000 boat at best, i paid $2000 for it,if i were to do as you say and buy a new mast it would not be a good deal at all. This mast is very easily repairable by anyone able to do their own thinking. Im a boatbuilder by trade and this repair is a piece of cake and will cost me an afternoon and no money, just materials i have on hand. Im well aware that the mast is a compression member and all i need to do is prevent the depression from being able to buckle inward which is easily accomplished with an external sleeve. It is no different than an internal sleeve which is very common on mast repairs,in fact my Lindenberg has such a sleeve where there is a dent from installing the keel stepped mast.
Steve.

 

Cut the damaged parts out and sleeve the upper mast.
Then modify the tabernacle with a custom stainless weldment to add the lost height. The boom will have to drop that distance relative to its old position against the mast, but that shouldn't be a problem. By what you say only 4"-5" or so of mast needs to be cut out. If the remaining mast is undamaged, this should work.
Alternately, the cabin roof under the tabernacle could be raised with stacked plywood set in epoxy and glassed in.

 

Both areas can be straightened and sleeved. It's a common repair method and works well.

 

SteveW

Whether you boat cost $2, $2000 or $2m, doesn't affect the purpose of the mast. Ok, so you sleeve it, fine. So, when there is a high compression load into the mast, how does the load go from upper part of mast to the lower via the sleeve? It goes through the method of attachment of the sleeve to the mast.

Whether you weld it or rivet it, the lower part will no longer be in-plane, it will be slightly eccentric, as shall be the applied load. As such the mast will no longer be able to act as a compression member, the applied load is now bending the mast, as it is no longer acting as a pure strut!

So your mast will now bend, what load is it designed to withstand in bending, probably not a lot. The welding/riveting will reduce the strength locally and add stress concentrations; so the attachment is the weak link, especially with regards to fatigue and the high salinity environment that the joint is now exposed to. The original design stress is now seriously reduced.

I wont go on, but despite the fact this is a "common" repair, it is not a life long repair nor one which I personally would feel safe with in a F9 gale. It is more of the "to get me home" type of repair. To think otherwise, is simply asking for trouble.

But you asked for advice/comments you have a range of them above. Take your pick, I'm only giving my tuppence penny worth.

 

I've seen, surveyed and repaired myself, masts with sleeves, that have known 20 years of additional service. Sleeves are in fact how you get a mast of longer dimensions then the extruder permits. So, I guess we've all been wrong all these years and all we had to do was pay attention to you. Ad Hoc you should speak what you know as opposed to what you think you know. I would think accurate information is more important then well defended opinion, in an environment such as this. Out of curiosity, how do you get 65' masts with a 45' extrusion limit?

 

PAR
"...So, I guess we've all been wrong all these years ...", where do I say you are all wrong, I don't. I said I would not recommend it, for stated reasons.
The method of the sleeve, its location and it thickness (for starters) as well as the grades and expected design loads all play a part..none of which have been furnished in this "brief of a post" to truly ascertain the applicability of such a sleeve. So without such information one can only generalise, which I did.

In engineering, anything can be made to work, but at a cost, and also reflected in the service history and predicted service history, again, not cited.

Ive seen struts buckles owing to very slight eccentric loads as well as very poor repair jobs done on them, as per reasons mentioned above. So your "experience" of such jobs differs from mine, and this means..??? Nothing, just that, different.

If you wish to recommend this, doesn't bother me one bit, i wouldn't.

The extrusion limit is governed by the quality of the mill, ie the max length of table they ahve during extrusion and of course the cost. Not sure who or where you obtain yours, but it is not difficult to get long extrusions if you want them. (Sapa quote between 25~50m). But more often than not it depends whether you can actually transport a mast that long and hence, wish to pay a higher cost for it.

 

What are the dimensions of the mast and the sail area? Many boats have grossly oversized masts. If you have a racing rig dimensioned to the lightest possible section, it would need a different repair and care.

 

Par, thank you, its always nice to hear from someone else with actual experience and you consistently show that. This is a realatively minor problem,as i mentioned it is not possible to sleeve it from the inside in the typical way as i would need to cut the mast off at that location to gain access which would be making a large job out of a small one which is why i will do it on the outside, on the plus side i am able to do a very good job of preparing and glueing the external sleeve. I would be a lot more concerned if it were a sharp deep dent but its not,i have seen boats in our yard with bigger dents that have been sailing for years with no repair. As to sleeves being used on new masts,we replaced the mast on a newer Hunter last year with in mast furling and both the old and new masts were sleeved,incidently,the mast had fallen down while the boat was on the hard for the winter and amazingly missed all the surrounding boats.
Alan, im quite comfortable doing a minimal repair in both areas,i first considered cutting the bottom 2" off which would of course require shortening the shrouds but disregarded that in favor of just straightening the thing and installing the external sleeves for simplicity and cost, it will either work or if it doesnt, its down where i can keep an eye on it and it wont cause the mast to come down,i believe it will work as well as an internal sleeve without the complexity and it will have no cost.
Ad Hoc,the reason i posted this thread was not to ask opinions on whether it repairable or not,it is for anyone with any skills,what i was hoping was that there may be an actual sparmaker on here that could give a useful opinion on if i would actually need to sleeve the upper depression at all,in view of the fact that as i have said,ive seen bigger dents on masts that have been sailing like that for years.It looks like i will do the repairs as planned.I will be using a toughened pressmold epoxy from Hardman chemicals,its nasty stuff but by far the best ive ever used where metals are involved.
Thank you,Steve.

 

Steve W
"..the reason i posted this thread was not to ask opinions on whether it repairable or not.."
I understand and appreciate that. My view is just different to others (from my own differing experience), that is all. This is not to say it wont work, anecdotal evidence suggests this (but without actual facts difficult to really quantify to their "effectiveness". However, i still stand by my first posting, i wouldn't do it if it were my boat.

 

Steve, your repair strategy seems sound. The location of the dent has me concerned, it's in a bad spot. This seems typical Perry design work,a moderate SA/D (17.3) and moderate D/L (210), so loads will not be very high, but the mast exhibits a fair amount of bend above the spreader, so I'd sleeve the dent.



She's not going to run down any modern 27 footers (unless it's blowing like hell) so maybe not cranking in a lot of backstay tension from here on out, would be a wise choice.

 

Ok, i just went and looked at the mast to refresh my memory, the dent/depression,(it doesnt have a sharp crease) is 38" below the forestay attatchment point and is about 3"x3" but is a lot shallower than i thought,only
about 1/32"+.the mast section is an Isomat NG 31 6.28" x 4.10" wall thickness is .095" and the J35 mast sidewall which i am useing for the external sleeve is approximatly 5/32".My stratergy is only to prevent the dent from being able to collapse so i am not going to go real big with the sleeve , just enough to cover the dent plus a bit, 6" high x 4" wide so i dont affect the bend characteristics too much,i will put a matching one on the undamaged side to keep it balanced, lots of rivets and epoxy and all will be good,she looks good in that photo Par,looks a lot better in the water,you are right, shes no speedster, PHRF says she is 51 secs/mile slower than my Lindenberg 26.
Steve.

 

Steve W

The NG31 is a 6061-T6 alloy, therefore ensure your rivets are good quality ally (preferably the same as the mast) or stainless (even Monel), nothing cheap nor plated, otherwise you'll get major corrosion issues which has it own knock on affects. Using ally/stainless will minimise any potential problems.
Don't have the rivets too close, approx 3 diameters spacings as a minimum, to prevent any 'tearing' under high loads.