Mast materials and Specifications

  • 12 Feb 2014 19:05
    Reply # 1496683 on 1306051

    Those who follow this forum will be well aware that Lexia lost her foremast and rig in last years OSTAR.  We, that is Lexia and I, got back safely and had a new foremast built and installed by the then Atlantic Spars of Brixham, so quickly that I was able to set out again, although I later retired.  Much of this is reported in this forum and Magazine Issue 63.

    (I should perhaps write here that the foremast was 4" dia at the deck, not the 3 1/2 " that I reported at the time.  It was sleeved on the lower section.  The upper section was tapered almost to a very narrow dia and very whippy.  Robin Blain of Sunbird Marine Services does not have any further technical specification.) 

    (The replacement foremast was made with a lower at 5" dia at 3 mm thickness with a 3 mm sleeve, and a top section of 4" dia 3 mm thickness unsleeved.  It is thus stepped between the top and bottom but this step has a sloped collar to reduce any drag on lowering sail.  This seems to work satisfactorily.) 

    I am now very seriously considering replacing Lexia's main mast, which like the foremast is original and 36 years old.  It is not an easy decision, not least because it will be a significant cost, and also because it is impossible to state categorically that it needs to be replaced.  (Sunbird Marine Services is not Boeing!)  The only certainty would be if I don't replace the main mast and it does fail, and then I would be certain that I should  have done something about it. 

    I should say something about my general approach to junk rig boats and masts.  I am well aware that some, indeed many members make their own boats and rigs and masts, or modify existing boats with other rigs.  This has not been my approach.  We bought a Sunbird 32 which, although pretty old, was designed and produced commercially as a junk rigged schooner.  I do not have the time or inclination to knit my own. 

    When it came to replacing the foremast I went in search of a commercial solution and that is what I will do for the mainmast.  I am well aware that there are members whose approach to their mast ranges from setting out into the forest with a small axe and emerging with a large pole .... to manufacturing a mast and spars from carbon fibre. 

    If Lexia is to have a new main mast it will be from a commercial supplier and almost certainly in aluminium alloy. 

    A word then about the likely supplier.  Charlie Hutton worked from 1968 to 1981 in the design office of Ian Proctor Metal Masts.  In 1982 he set up his own business, Atlantic Spars, in Devon.  In 2008, because he was 'getting on a bit', Charlie sold the business as a flourishing concern but then worked for the new owner as designer.  This was the position when Atlantic Spars designed, manufactured and fitted the new foremast for Lexia in mid 2013. 

    (Almost incidentally, Atlantic Spars had previously made a new main mast for Dennis Sidebotham and Janvier Aquila, a similar sized junk rigged schooner and Dennis reported that he was pleased with the dealings and the result.  Janvier Aquila is about the same age as Lexia and had, I think, a similar original Neeldlespar mainmast which came down in not very strong wind just off Plymouth.) 

    Later in 2013 Atlantic Spars went into Administration.  The whys and wherefores of that are irrelevant to my story here I think. 

    Charlie and Dan, another employee of Atlantic Spars, have since set up a Brixham branch of Petersen Custom Rigging, a company based in the North East of England.  I was impressed by Charlie and Dan in my earlier dealings with them and will probably throw in my lot with them again. 

    I  think that we can take it as a given that Charlie Hutton knows a thing or two about aluminium spars. 

    Now some information about Lexia and her spars. 

    32' 6" LOA.  26' 4" LWL  Beam 10' 4"  Draft 4' 0"

    Design Displacement 10,000 lbs.  Ballast 3,600 lbs

    Long shallow fin encapsulated fin keel and skeg mounted rudder.

    Foresail 217 sq ft.  Mainsail 337 sq ft.

    Foremast originally 4" OD at deck, now 5".

    Current Mainmast 5" OD at deck.  By Needlespar 1978.  Bottom part of mast understood to be sleeved.  Top part tapered, swaged ?  Very narrow at top.  Top and bottom joined with insert sleeve and "glue" ? No more details currently available. 

    Robin Blain states that it is accepted that the foremast on such a boat has a harder life than the mainmast.  Certainly on Lexia it was the foremast that failed, but on Janvier Aquila it was the main mast.

    The cone through the deck for the main mast partners will reasonably accept a mast up to 5.5 inches.  It would just accept a 6 inch mast but with very little clearance.  The bottom of the cone might be trimmed to make it bigger but that would decrease its depth and hence its strength and its depth for any Spartight type compound. 

    Charlie has produced quotations for three possible design specs.  All specify Al 6082 T6. Silver anodised. 

    Some general considerations. 

    Charlie can get tube up to a max length of 5 metres, so any mast made by him will be a construction. 

    5" OD available at 3 mm or 6 mm wall

    5.5" OD available at 6 mm wall but not 3 mm wall.

    The three designs are in increasing strength ( / stiffness ? ) but in increasing weight and cost.

    The first design is the same OD bottom to top, which is more attractive than having a step, albeit a step with a tapered cone. 

    Tube 5" x 3 mm.  10.00 m above deck.  2.14 bury.

    Internal doubler 3 mm to 3.66 m above deck.

    Charlie's method for the doubler is to take a tube of the same OD and thickness as the mast and to cut a section out of the length of it.  The doubler is then tightened to a smaller dia and greased and then hauled into the main tube using a TIRFOR winch.  It will have a remaining split of approx 4 mm.  The doubler is then joined to the main tube by drilling and rivetting both.  As indeed are the sections of tube used to make sufficient length from the 5 m max length tubes. 

    I know that this statement on drilling holes in mast tubes will produce shock and horror amongst some of the members.  (Shades of a Bateman cartoon!)  Charlie's response is that such rivetting is not done near the partners.  Also he states that anyone who states that one must never rivet a mast together might like to look out of the window of an airliner at the rivetted construction of the wing. 

    Charlie also fits an aluminium tube internal conduit for electrical wires, rivetted to the main mast but not rivetted near the deck.  Again Bateman cartoon shock horror.  I put to Charlie some of the suggestions made by members made by members as alternatives to stop electrical wires banging about inside the mast.  His comment was that such solutions tend to be water traps which may encourage corrosion. 

    The second design is for a stepped mast with a bottom section of 5" x 6mm wall to 3.8 m above deck and a top section of 42 x 3 mm wall. 

    The bottom of the top section has a plug to fit the internal dia of the bottom section.  The join is made with a plug with an upwards facing cone in the top of the bottom section. 

    The third design uses 5.5 " x 6 mm bottom tube and 4.5 " x 3 mm top tube. 

     

    My current inclination is to go with the first ie the cheapest and lightest design.  It is the same OD as the original but Charlie will be at least as strong and certainly it will be at the start of its fatigue life.  It is the same design as the mast for Janvier Aquila. 

     

    I am of course open to comments.  And no I don't think that I will be setting off into the forest with my little axe, or knitting a carbon fibre tube!

    If nothing else is achieved it may be useful for other members to know how this member is currently is addressing this issue. 

     

     

     

     

     

     

     

     

     

  • 02 Feb 2014 00:02
    Reply # 1488255 on 1306051
    The masts on Arcadian are fiberglass and were purchased second hand from a boat called Aphrodite. They were originally used in an Aero rig with double sided sails and aluminium aerofoil shaped  "battens" sleeved over the masts. The masts are 10 inch diameter for the full length of the mast, and vary from 3/4 inch wall thickness at the deck to 1/4 inch at the top. The foremast is 44 feet long and has a bury of about five feet setting a sail of 500 square feet. The main mast is fifty two feet long and has a bury of six foot six inches setting a sail of 700 square feet. 
       In two summers of sailing we have had no problems with the masts. In winds of 25 knots under full sail to windward the masts assume a visible curve with the tops being displaced by approximately two feet. This does not appear to affect their efficiency and causes no problems. At anchor in 50 knot winds the masts develop a whipping action that can become a bit disconcerting but is controllable by taking a spare halyard, attach it to a cleat at a 20 plus degree angle to the mast and tension it up. An alternative may be to tie the spare halyards together and tension the one mast against the other, I have not tried this so far so don't know if it will work.
       The non tapered masts are not the prettiest out there but mean that I can use fixed luff parrels thereby reducing the amount of running rigging needed.
        I have not had experience so far in motoring into a head sea but anticipate that it will cause whipping of the masts, although this may be controllable by hardening in on the lazy jacks.
    Last modified: 02 Feb 2014 00:45 | Anonymous member
  • 31 Jan 2014 16:59
    Reply # 1487464 on 1306051
    Phil,
    The JRA used to own a dayboat of this size (you might find a reference to her in one of the old newsletters; her name was Ariel, I think). If my memory serves, her mast was 4" x .125" wall, and she made some offshore passages in the Bristol Channel, under a western lugsail rig, before she was converted to junk rig. So I think that size would suit you, too. Bigger diameter + thinner wall is more efficient, in terms of strength & stiffness versus weight, so I think you're right in rejecting the thicker walled pipe, in this case.
  • 31 Jan 2014 06:20
    Reply # 1487247 on 1306051
    I've been a quiet member for the last couple of years catching what I can from the knowledge here and poking along with my conversion of a Com-pac 16. Aluminum is a new material for me. I built one successful wooden mast but this second one turned out heavier than I calculated so I cut size and staves from 19+ feet to 17+feet and left a panel out of the now completed sail. This reduced it to 5 sq ft less than the original basic rig. It was planned as a mostly scaled up version of Broremann's. I regret reducing the sail and I still have the 7th panel and a sewing machine. A taller hybrid mast may be just what the doctor ordered.

    The boat is 16ft (4.88m), wt. 1100Lbs (498kg), beam 6 ft (1.83m), draft 18in (.46m), ballast 450lbs (204kg) in the very shallow keel. The sail area would be 135 ft2 (12.5m2) with panel #7. The righting moment should be in the 230 range. My original goal was a mast that weighed about 32 lbs (14.5kg). It will be tabernacle mounted. The boat has a very small cabin, a self bailing cockpit and will be used for lake and coastal day sailing.

    I'm thinking a base piece of 6061 t6 tubing 4''x .125'' (102mm x 3.18 mm) at 1.9lbs/ ft (.863kg) would have enough diameter and the wall would be just enough for the planned use although it falls well below (above number wise) the specs in David's posted formula for a cruising boat robust mast.  .125 and .250 are the more easily available and reasonably priced wall sizes. I got a quote on less common wall in a 3.5'' x .188'' (89mm x 4.78 mm) piece of tubing that was priced out of range at about 3 times the cost of the two more locally available common dimensions. 6061 t6 looks to be 10 or 12% less strong than 6082 t6 but that has very limited availability in the states. The best price I got was on a suggested piece of 3'' ''structural pipe'' 6061 t6, 3.5x .216'' (5.5 mm). Don't know how different it may be structurally from tubing but at 2.64lbs/ft (1.2kg) and added wood section it would make a heavy mast

    I'd like to be able to go with the lighter thinner wall of .125'' / 3.18mm. 3.5'' would be easy to work with and handle but I'm guessing 4'' diameter especially at that wall thickness would be the minimum. This is part comparison with Froken Sorenson, part beginning to understand more about the subject, mostly concern about wall thickness and part guess.

  • 04 Jan 2014 11:37
    Reply # 1467696 on 1306051
    I'm nearing the point when I'll have to decide what to make the masts from, and it's a matter of tradeoffs like most things to do with boats. The best points of grp masts would be low cost, and low maintenance. When I built this boat I was 30ish and going up my wooden mast to do routine maintenance was something I didn't mind, it was actually kind of fun. Now I'm twice as old, retiring next year, and refitting the boat for an 80ish sailor, as I hope to be some day. 

    My style of sailing is like Grahams, I have a Sabb 2J that is newly rebuilt, it sips fuel, and I don't mind motorsailing when the wind doesn't cooperate. Robustness is more important to me than speed or windward efficiency. I love wood, that's what my boat is built of. But I can't see myself as a geriatric sailor, up the mast in a bosuns chair with a pot of varnish.

    At the moment grp seems like the best choice overall. I would have to use a section about equal to that of a hollow wooden mast, and add some extra material for stiffness. And I will definitely add some extra length for sufficient drift, thank you for that suggestion.

    So unless I become aware of some fatal flaw in the idea, I think I'll finalize my plans and place the order.

  • 03 Jan 2014 23:22
    Reply # 1467522 on 1306051
    Hi Robert.  I am not an engineer either and used the empirical method to choose scantlings for my aluminium mast (sail area 35.7 sq m).  I looked at David Tyler's main mast scantlings on Tystie, which is a well-tested ocean voyager, and went looking for a mast of similar dimensions.  It wasn't easy to find anything suitable in Australia but eventually I found the bottom half of a giant flagpole at Federation Flagpoles in Adelaide, overall length 10.5m.  The section is 200mm at the base and 110mm at the truck, spun tapered with a wall thickness of 5mm all the way.

    I have pressed the boat extremely hard in order to test how much it can take and think the masthead flexes about 100 - 150mm normally.  My only reservation has been when motorsailing in light winds and sloppy seas and the yard starts to swing.  Because I have only got a small amount of drift (300mm) between halyard blocks, this puts a severe wrenching load on the masthead.  I resolve this by dropping one panel to increase the drift, which solves the problem.  An extra 500mm mast height would be ideal.  As a sailor who has already circumnavigated, you will know that cautious seamanship is a part of the equation that engineers cannot factor in!

    I'd love a laminated timber mast, sheathed in epoxy resin and glass cloth, as I find my aluminium mast a bit noisy.  Steel masts probably share the same characteristic but they are cheap, easy to manufacture to individual specifications, and less prone to fatigue and corrosion than aluminium if they are carefully protected (galvanising, epoxy painting etc). The fibreglass masts you are contemplating are probably strong enough, although their diameter is large.  Not much larger than you'd end up with in a timber mast though.  (My mast, if built to PJR specifications in solid timber, would be 10 inches at the partners.)  A smaller diameter would certainly be more efficient to windward in flat water but it is not the only factor to consider in the open sea, where hull design and sea state play equal roles in determining daily runs.  Once you crack off to a close reach, which is as close as I ever go in the open sea, it won't matter at all.  If I NEED to claw to windward on the coast, I can do it, just, as I have a heavy, short, fat hull, but I am happy to motorsail.  I am an ocean sailor, though, and I believe in everything being stout! If I had a lightweight, fin-keeled, fast hull and a passion for racing, then I'd be looking for the most efficient mast and sail to go with it.  Horses for courses.  
  • 03 Jan 2014 22:08
    Reply # 1467472 on 1467111
    Deleted user
    Robert Leask wrote:I've been doing my best as a non-engineer to evaluate these grp masts and at this point I've pretty well exhausted all the information I can gather from the internet. I know carbon is far superior to glass fibre, 3 or 4 times as stiff and strong. That sounds discouraging until you compare the characteristics of, say, douglas fir, and given the elastic modulus and tensile strength of commonly used spar timbers, wood looks like a non-starter, which makes clear that the engineering approach has it's limitations. 
    What makes wood great is there is no stress fatigue, the stuff can flex to and tho' for millennia and not fracture. AFAIK there's no man made substitute which has that property. The caveat though is to keep the stuff dry, so it doesnt rot, usually by sheaving in fibreglass.
  • 03 Jan 2014 07:47
    Reply # 1467126 on 1467111
    Robert Leask wrote:
    These poles are priced reasonably enough that if they failed or proved too whippy it wouldn't break the bank. My main question now is: how whippy is too much? When you experienced sailors are in heavy sailing conditions how much do your mastheads move?

    I've never actually seen mine move, although they must. It is obviously a very small amount. They certainly do not whip at all. My masts are steel and have been described in quite a few post in these forums.

    The calculated deflection for my main mast was 315mm with full sail up in 40kts of wind. So for all practicable purposes they are ridged.



  • 03 Jan 2014 06:23
    Reply # 1467111 on 1306051
    I've been doing my best as a non-engineer to evaluate these grp masts and at this point I've pretty well exhausted all the information I can gather from the internet. I know carbon is far superior to glass fibre, 3 or 4 times as stiff and strong. That sounds discouraging until you compare the characteristics of, say, douglas fir, and given the elastic modulus and tensile strength of commonly used spar timbers, wood looks like a non-starter, which makes clear that the engineering approach has it's limitations. 

    These poles are priced reasonably enough that if they failed or proved too whippy it wouldn't break the bank. My main question now is: how whippy is too much? When you experienced sailors are in heavy sailing conditions how much do your mastheads move?

    I do know that grp spars from Shakespeare have been used successfully and I have compared the specs of those with the ones from Whatley that I'm considering, and the Whatley ones are significantly stiffer and stronger. I see the main drawback of using a grp pole would be the need for a heavier section, and more drag on the "bad tack". But I think the section of this mast would be about the same as for a hollow douglas fir mast, which I would use as my second choice.
    Last modified: 03 Jan 2014 06:25 | Anonymous member
  • 03 Jan 2014 02:54
    Reply # 1467053 on 1466890
    Brian Kerslake wrote:Hi Peter in Canada.

    I'm yer Webmaster and am just posting to say 'Welcome' and that this is a good spot to post on this topic....

    Dear Webmaster,

    The poor mans name is Robert not Peter (we have plenty of those but this is not one of them :-) )...


    Robert (who is not Peter) welcome to the site, hope you are enjoying it. As our dear Webmaster say's, it's quiet right now but that's owing to the season (and the English members all outside trying to prevent their boats being blown away :-) ) in due course things will liven up again.

       " ...there is nothing - absolutely nothing - half so much worth doing as simply messing about in junk-rigged boats" 
                                                               - the Chinese Water Rat

                                                              Site contents © the Junk Rig Association and/or individual authors

Powered by Wild Apricot Membership Software