Seaward 23 Broken Mast Repair

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I just don’t get it. I like to think of myself as a critical thinker having been a physician in a prior life. And I have completed many boat building and repairing projects over the past 50 years in wood, fiberglass, carbon fiber, polyester resin and epoxy but I just don’t understand the engineering regarding the 1996 Seaward “carbon fiber” mast. I do understand how sexy carbon fiber sounds and have seen the genuine item (just Google “carbon fiber mast”) on Tornados and other one design boats so I do understand why this mast was marketed as “carbon fiber” but it just does not appear to have been built like the real thing.

The mast broke at the base as a result of lateral pressure and compression. The down wind low pressure side buckled and crushed at the point where the aluminum slide pipe control line exited the spar. The light gauge SS slider line exit fitting was bent in half and mangled. The first question is why was the integrity of the mast compromised at this point by mounting the slider exit fitting here?

The mast appears to have been constructed over a long male internal mold. The mold seems to have been wrapped with common, light weight 0/90 fiberglass cloth and then wound with carbon fiber off a spool at a tangent or 90 degree angle to the length of the spar. This would give some dimensional stability to the round section of the spar but virtually no longitudinal resistance to bending (minimal structural support for compression or tension). The only fibers running along the lines of stress appear to be the kerneled glass fibers in the light weight cloth 0/90 degree woven cloth. I am amazed the spar lasted as long as it did.

The spar is repaired using an internal aluminum pipe machined to the dimensions of the aluminum slider pipe used to attach the spar to the boat. This pipe fits INSIDE the existing larger lower mast base section and extends down into it about 2”. The two machine screws just below the top of the main lower mast section that limit the upper range of the aluminum slider pipe are removed. The new repair sleeve inside the larger aluminum mast base determines the upper limit of the sliding mast mounting sleeve. As the fiberglass mast sections start OUTSIDE the lower mast base section, there is approximately a 3/8” gap between the OD of the repair sleeve and the ID of the fiberglass section of the mast. This void is filled with woven roving as a non structural but non compressible element of the repair. The sleeve is wrapped with woven roving about 2” above it’s base and slightly tapered to allow easier later fitting into the upper fiberglass mast section. The 2” bare aluminum section of the repair sleeve fit into and are bonded to the larger lower main mast aluminum mounting section. Angle irons are strapped to the lower section to allow for proper indexing and alignment of the repair assembly to the lower mast section. The sleeve/fiberglass assembly is then bonded into the lower mast stub using a viscous mixture of epoxy and cotton fibers. This is allowed a minimal cure time.

The indexing angle irons are moved to the upper tapered fiberglass spar section. After a dry trial fitting, the exposed areas of the sleeve/glass assembly are coated with a thicker mixture of epoxy/cotton fibers and the lower section is pressed into the upper section and aligned properly (sail track aft, slider line aperture forward).

The large void area where the crushed glass/carbon lay-up was removed is filled with multiple layers of woven roving until the surface is in line with the OD of the fiberglass spar. The lower section of the spar is then sanded in preparation for mechanical bonding of the outer structural repair.

The prepared mast section is coated with a mixture of epoxy and cotton fibers to “level” the lumpy mast surface that resulted from the original carbon tow tangental wrapping. This allows the unidirectional 3” wide aircraft tape to remain in straighter alignment. This material is available through Aircraft Spruce company. Once the epoxy “icing” becomes stiff, the unidirectional tape is applied from the base of the fiberglass spar to 18” above the upper limit of the internal aluminum sleeve. Several layers of varying length are used and “feathered” at the upper limit to avoid creating a hard stiff ring where the mast could fail again. These unidirectional fibers are then covered with one layer of biaxial (45/45) light fiberglass cloth to bind them together. Once cured, washed and lightly sanded, the repair is painted with epoxy spray paint.

The slider pipe exit fitting and cleat are then mounted on the leading edge of the spar. Note that the line exit and cleat mounting are both through the internal structural aluminum sleeve.

Do not try this technique at home. I am a backyard boat builder with no engineering background. If you wish to repair your broken spar I suggest you contact a marine architect and pay a lot of money to have proper engineering drawings produced. When this mast fails again, I believe it will fail above the repair. I don’t know if this failure will be during the first sail or in 15 years but it is bound to happen given the construction of the original spar.


Repair Sleeve 24’ OD machined to match Slider Sleeve     $240
West System Epoxy & 205/206 Hardeners                 $120
Chopped Glass, Cotton Fibers                            $ 30
Woven Roving, Aircraft 3” Unidirectional Glass              $160
Gloves, Masks, Brushes, Containers, Mixing Sticks, etc.      $ 40
Grinding Disks, Sandpaper, Grinder Bits, other abrasives    $ 60
Indexing Angle Irons, Large Hose Clamps                   $ 50
SS Pop Rivets                                          $ 10
Electric Power                                          $ 40

TOTAL                                                $750

Shop rates for labor will vary so if such a repair is attempted through a professional repair facility you may expect an additional 6 to 8 hours of labor. Shop rates could vary between $50/hr and $100/hr. Expect to pay between $1,200 and $1,600 for the actual repair in addition to the professional services and drawings from the marine architect.

Roger H Strube, MD





































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