aluminum masts

[sscoville]

I initially built 3" diameter solid wood masts for my BRS 17 and now want to convert to aluminum.  I haven't yet located my old set of plans to find the specs on the aluminum and how the parts go together, but I seem to remember that the sections are joined using fiberglass tape to make collars, but when doing a search of this forum I found nothing about this.  I did find a post about "reaming" the aluminum.  Can someone explain the how the masts are made from aluminum?

 

Also, as my masts' steps are made to fit 3" masts, the aluminum masts will be too small.  My plan is to build up the masts at their heel and top of the main mast tube and mizzen thwart using fiberglass tape, as opposed to installing a new mast tube, thwarts, etc.

[Joe Anderson]

Someone with more knowledge of the BRS 17 might chime in. My masts are larger but the idea is the same. I think the BRs 17 masts are two pieces. You need to build up a bushing on the smaller tube so it fits snugly into the larger.  Insert the tube about 12 inches maybe less for a BRS 17. You can wrap the tube with 3 inch tape dry to get an idea how many wraps of tape are required. I wet out the tape in a tray then wrapped the tube it is pretty messy but not as bad as it sounds. If the fit is too loose add more tape and epoxy when it is too tight start sanding. If you can manage to wrap the tape neatly and estimate the amount correctly it is pretty easy. Unfortunately it is one of those jobs you have figured out about the time you are finished.I wouldn't ream the aluminum.

 

 

[rmraya]

Hi,

 

I recently bought plans fro a Core Sound 17 and I'm still studying them and planning before building. I would appreciate if someone has a picture that shows how sail tracks are placed near the mast union and how the difference in diameter is handled in that case.  

 

Thanks in advance,

Rodolfo

[Howard]

What Joe said about fitting the bushings and collars.

 

For most masts of this size, the aluminum tubing is 6061 aluminum and you will use .0625" or .125" thickness tube, depending on the plans for your sized boat. The sizes they sell in this range are stepped in 1/4" outside diameter increments, so the gap that you need to fill between the inside diameter of the bottom tube and outside diameter of inner tube is either .0625 or .125". Typically, that will be 3 or 4 wraps of 3 or 4 inch tape for the .0625 tube and twice that for the .125 tube.  You will want to trim off the bumps created by the selved edge on the tape. An additional set of wraps of 1.5"  or 2" tape goes on the smaller diameter tube on top to act as a stop. The thickness of this stop collar needs to be at least as wide as the tube end it rests upon. All the weight and force of the halyards and downhauls is forcing this section into compression, so don't take this lightly. This is also a good reason not to ream it. You don't want a sharp edge taking the load. The fit should be snug enough to not rattle around, yet loose enough they won't jamb so you can take them apart. This assumes the masts are taken apart for transport. If they are left one piece, with sail tracks, the stop collar may not be needed.

 

Since your wooden masts were 3", you may be able to use 3" OD aluminum masts also, and progressively smaller mast sections above. Downside is it will add a slight amount of additional weight and will also be stiffer in the upper sections than designed. You may want to visit with Graham about this. It may work OK, or may not be what you want and worth the extra effort of working around the step down size.

 

As for transitioning a sail track over the joint, one solution is to build a ramp of thickened epoxy under the track above the transition joint. Gap is only 1/8" to 1/4", so is not a huge issue.

[Paul356]

Roguepaddler has excellent photos and description of the mast assembly in his book on making the 20.  See chapter XVI. 

http://www.roguepaddler.com/coresound20.htm

[rmraya]

Many thanks for the link. 

 

From the description in the mat building page, I assume that the mast is assembled from 3 pieces and never disassembled for transportation. Am I right?

 

Regards,

Rodolfo

[Hirilonde]

From the description in the mat building page, I assume that the mast is assembled from 3 pieces and never disassembled for transportation. Am I right?

That depends on the boat you are building.  My Spindrift mast comes apart a lot.

[ecgossett]

I put a couple of simple rivets in mine to keep sections from coming apart. With the fiberglass collars, the aluminum sections are very tight together, and if you add on a track it does even more for keeping it together. For track I used some 5400 caulk for smoothing from section to section for track. I've never had any problem with aluminam rivets on track, and two years later having popped a couple out for inspection I saw no sights of corrosion on SS track.

 

If you are looking for sections I bought the 2" & 2.25" at www.amazon.com; the 2.5" more  local suppliers had.

 

I had several people who thought I should just take the 2.5" x 20' sections and use them as a straight mast. However, when comparing weights I was glad I went the harder way. The sections have noticeable weight differences, and together the whole thing is almost effortless to put up.

[sscoville]

I believe the BRS 17 calls for two aluminum sections and the a wooden section.  I have laced sails, so I won't be using a track.  I just need to figure out the dimensions of the aluminum pieces.  I have my plans somewhere. 

 

Does anyone see a problem with my idea to build up the masts to fit my existing steps and tubing?

[Hirilonde]

Does anyone see a problem with my idea to build up the masts to fit my existing steps and tubing?

 

I don't see any issue.  You could also make inserts for the step and partner.  Either will work.

[sscoville]

My plans call for the bottom sections to be made from 8' x 2.5" x .083 tubing and the upper secction to be made from 2.25" OD.  I cannot find the 2.5 x .083 and I have a note that Graham previous told me that 2.5" x .125 could be substituted.  I see, however, that this has an inside diameter of  2.25".  It seems obvious that the upper section with the 2.25 OD will not fit.  Am I missing something?  I don't know what the inside diamter of the .083 would be as I haven't found any.

[Peter HK]

I also couldn't get the smaller wall thickness tubing and used the 0.125. It's a common issue which is why you've heard about reaming the aluminium tube to ensure the 2.25 in dia tube fits.  

Here's a photo of (boatbuilder) Charlie Jones' reamer..Just pack under the corners to get the right diameter.

 

untitled.bmp

 

Peter HK

[sscoville]

I suspected that was the story behind the reamer. Thanks!

[sscoville]

So are the glass collars still necessary?

[Peter HK]

No. It's a tight fit. I did make collars for the wooden topmast in my 3 piece mast.

 

Peter HK

[sscoville]

And no stop collar either?

[Peter HK]

No. I epoxied mine together and the screws holding the track on go through both tubes at the overlap.

Peter HK

[sscoville]

Well, I recieved my aluminum and was able to work the smaller one into the larger one just by hand, without any reaming.  I am considering simply putting some unthickened epoxy on the smaller one, sliding it in 9 inches and then applying some thickened epoxy at the outside joint. Then, for extra assurance, I was going to put two screws through each section at the overlap.  Is there any reason to be concerned about the tight fit and expansion?  I would assume the tubes would expand and contract at the same rate.

 

Also, they are currently stuck together, though they went in easily enough.  I'm going to heat the larger tube a bit and see if I can slide the smaller ones out.

 

Finally, how should I clean the outside of the aluminum so I don't always turn my hands black when I handle them?

[sscoville]

Well my new masts are basically finished. I may paint the wood sections at some point. I laced my sails on and am concerned that my lacing may chafe where the two aluminum sections join. Anyone had a problem with this?