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This article was published in

Good-old-boat

  March 2017

   The first indication there was any problem with BRITANNIA’S bowsprit was when I was hoisted up the foremast using the electric windlass which was bolted on top of the bowsprit. The operator mentioned the windlass “moved” as the load came on the winding drum.

   When I came down the mast I saw what he was talking about, because the windlass was noticeably out of square on the bowsprit. Clearly something was amiss, although I couldn’t see anything wrong with the painted wooden bowsprit. I checked the four bolts securing the windlass through the foredeck, and they were nicely tight.

rotten-bowsprit   On deck again, it didn’t take but a few minutes probing with a screwdriver to realize there was a serious soft wood problem beneath the windlass.

   I removed the four long windlass securing studs, and brought a load of rotten wood out with them. Further scouring with a chisel and electric cutter revealed extensive rot in the nearly ten foot long bowsprit.

   At first I hoped it would be possible to repair the ‘sprit in-situ, by scarfing some new planks in to replace the damaged ones. But that was ruled out as I scoured more and more soft wood from the interior of the spar. I gave up after a length of 38 inches!

   Clearly, the boat needed a completely new bowsprit, either wood like the existing one, or perhaps a metal substitute.

   BRITANNIA’S bowsprit was a tapered lamination of nine wooden sections glued together. It measured nine feet six inches long, eight inches square at the heel and five inches square at the crance iron.

    Other owners of Down Easters told me how their ‘sprits were constructed, but they were all different with no consensus as to how strong a replacement needed to be. Surely, some said, it made sense to make another in wood, like the old one. What they didn’t know was that the previous owners log showed a new bowsprit had been installed in 2005. This did not persuade me towards a third wooden bowsprit for the boat.

   If I was to make a new bowsprit in anything other than wood it had to be at least as strong as the previous one.

   When analyzing forces on a bowsprit, there are a number of factors to consider. When under sail there is an upwards and sideways pull on the ‘sprit which varies depending on the point of sailing, the wind strength and of course, the size of the head sails. This pressure is resisted, mainly by the bobstay, (and in BRITANNIA’S case also a dolphin striker, which transmits some load into the bow), the bowsprit shrouds, and naturally the actual strength of the ‘sprit itself and how it is secured to the bow. If all fittings are correctly tensioned the opposing forces result in a mainly compression force, pushing the bowsprit backwards.

   These interactions would be fairly easy to calculate in a simple static force diagram. However, a boat under sail is hardly a static force and another major unknown factor is when the bow ‘scends’ into a head sea, plunging the complete pulpit into solid water. This imposes goodness knows what loads on the grating and the ‘sprit, and nobody, including a sailboat architect, could tell me what these might be.

   A friend loaned me Skene’s elements of yacht design. This had a small section on bobstays, but surprisingly nothing about bowsprits, but it does include the sentence, ”Since impact loads like head seas cannot be determined accurately, most designers apply a factor of three to five in their estimates.” That struck me as a pretty wide margin, and in other words it was all based on experience and perhaps destruction tests, none of which was helpful to me.

                                                               ALTERNATIVES AND ESTIMATES:

Bowsprit-drawing   I made a drawing of the existing bowsprit and sent it to three wooden boat builders, who all said they could “easily” make one in Douglas Fir. However, on seeing “the complexity of the job?” one declined to quote. Then came the next shock! One quote was $2875.00 and the other $3278.00! Apparently the wood had to be shipped from the Pacific North West—about as far as it could be from Florida, where BRITANNIA lay. Also, no actual time for completion was even mentioned by either builder, Allthough I specifically asked for it. It was obvious that none of these people really wanted the job.

   My next option was to see if I could buy the wood myself. I located a lumber supplier in Minnesota, (which I didn’t know was in the PNW?), who quoted $830.00 for four 2” inch thick finished straight grained planks of Douglas Fir, ten feet long and eight inches wide.

   Building a new ‘sprit myself was obviously the cheapest way, but a daunting task, First I had to glue and clamp the planks together, then shape the massive log, (about 200lbs and about as big as a railroad tie) into a taper, with a 4 inch perfectly round section on the end to carry the crance iron. Furthermore, all this would have to be done with hand tools, outside on the dock, because I had no covered facility. I have achieved some big projects on the boat, but this was just too much to consider.

   I decided to explore the possibility of having the thing fabricated in aluminum. After researching different types of aluminum plate I decided to specify 1/4 inch thick type 6061 structural aluminum. This is as-hard-as-nails and much stronger than regular aluminum. I didn’t consider stainless steel on the grounds of cost and weight.

   Luckily for me, my son-in-law is the senior patent attorney with a New York law firm, (which requires a high degree of engineering qualifications) and Jim offered advice on the aluminum design.

   The ‘sprit needed to be the same shape and size as the existing spar, so all the fittings would bolt back in the same place. I therefore designed a box section with a vertical central spine all the way along the inside. This formed an ‘I’ (eye) beam, which is a well known section for stiffness in both bending and compression.

   I was also interested in the weight of an aluminum ‘sprit against timber. Kiln dried Douglas Fir weighs roughly 35 lbs per cubit foot, and I calculated my existing ‘sprit was 3.24 cu ft. That made it about 113 lbs.

   The weight of 1/4 inch thick 6061 aluminum sheet is 3.56 Lbs per square foot. I worked out the square footage of each piece in the drawing, which all added up to 27.83 sq ft. This gave a weight of 99 lbs, including a round tube at the tip to carry the cranse iron.

   Two aluminum fabricating companies gave me estimates. One was $1525.00, including powder coating painting the bowsprit and crance iron. The other quote was $2200.00 in raw form. It won’t be difficult for boat owners to guess which was the ‘marine’ fabricator’s quote from Titusville, as opposed to a regular welding company near Orlando, Florida.

   After much deliberation I decided to have the new bowsprit made in aluminum and I gave the job to Twin City Welding, in St Cloud, near Orlando. David Lucey, the owner, had done work for me before and I knew the excellent quality of their welding. They also stocked the sheets and were very familiar with the welding characteristics of 6061. Another advantage was that they could start the job almost immediately. I also decided not to remove the old bowsprit until the new one arrived.

CONSTRUCTION.

Bowsprit-construction   After all the pieces had been sheered out of a 10 foot x 4 foot aluminum sheet the top and bottom sections were welded to the center spine. The bottom had been bent slightly to form the underneath taper towards the tip. A new staysail forestay bracket was also welded through a slot in the top plate. The original stainless steel bracket was bolted through the deck, so my design avoided two more holes through the ‘sprit and deck.Heel-plate

   A 4 inch diameter tube was welded on the tip, to carry the heavy bronze crance iron, which itself weighed 26 Lbs.

Roger-and-bowsprit   The two sides were then welded to the top and bottom to complete the box section. This resulted in a very stiff spar, which looked magnificent in it’s new dark blue livery to match the topside stripe of the boat. It had been exactly two weeks from placing the order. The new ‘sprit weighed 96 Lbs. I was 2 Lbs out in my calculation!

   I designed the heel plate to be screwed on the end of the bowsprit and removable, so I could reach through to bolt it to the two samson posts (bitts). sprit-removed

   I drilled two 3/8 inch holes in the bottom of the spit, near the heel plate, to drain any water which might find it’s way into the interior.

   At this point I supported the pulpit and grating with halyards from the foremast, which saved removing these cumbersome items. Next I withdrew the eight long threaded rods which held the pulpit and grating through the old bowsprit, along with the threaded rods holding the bowsprit to the deck and samson posts. Then, with a few willing helpers the damaged bowsprit was levered clear from the bow and pulpit.

   BRITANNIA looked very forlorn without her majestic ‘sprit, which gives character to any clipper bow.

   The wooden bowsprit weighed 116 Lbs, allowing for the missing rotten sections. I was 3 Lbs too heavy with that calculation.

   I cleaned up the stem head, filled all the old holes and re-painted the area, We were now ready to install the new bowsprit.

                                             INSTALLING.

   First, the Maxwell windlass was positioned on top of the bowsprit with through-bolts, which helped pull the bowsprit down on the deck. Three heavy 2/0 AWG electrical wires for the windlass motor also came up through the ‘sprit.

   Holes were then piloted sideways though the samson post bolt holes and the posts bolted inside the tube. The gratings and pulpit were then re-positioned and holes piloted through from both sides and bolted together using the old 3/8 inch stainless threaded studs. I upgraded the threaded studs which carried the two bow rollers to solid rod.

   All the holes were caulked liberally with 3M 5000.

   The crance iron, which had been powder coated white, was pushed on its tube, and the jib stay, forestay, bobstay and shrouds relocated and tensioned. Both anchors were then hauled back into their rollers.

  I had to make 12 one inch teak plugs, and six 1 1/4 inch plugs to fill the holes in the grating and samson post. I make this by hand because I didn’t have a plug cutted for those sizes.

   All this heaving and maneuvering was done with the boat in the water and the bow sticking over the dock. This was easier, and cheaper, than lifting the boat, because we didn’t need scaffolding or ladders, as we would have on the hard.

   The reassembly operation took three days, during which the spit was removed and replaced for adjustments seven times.

Bowsprit-test   I wondered how we might test the new structure. The ultimate test would be a sea-trial in heavy weather, but I also decided to conduct a simple static test, by bowsing down the bowsprit to see what happened.

   I wanted to test the bowsprit, not the jib and staysail stays, so I disconnected them both. With only the bobstay and shrouds attached to the crance iron I lowered the 60 Lbs CQR over the bow roller and hooked it under the dock, directly below. Then I measured the distance from the cranse irion to the dock.

finished-bowsprit    I then tensioned the chain with the windlass, which I was pleased to see never even budged. This pulled the bow downwards and the bobstay bracket disappeared under water. A second touch on the winch pulled the bow down even further and the chain was now bar tight. Amazingly, the bobstay also remained taught—which would have gone slack if there had been any bending in the ‘sprit.

   Another partial turn on the winch resulted in ominous groans from the dock timbers, so I quickly measured the drop, then slacked it all off. The boat had been dragged down 7”.  Hauling a beamy boat down this far displaces considerable weight of water and imposed some impressive loads on the bowsprit, but there was absolutely no evidence of movement, or paint chipping, anywhere along the new bowsprit.

  On seeing the finished result Jim wrote. “Based on the back-of-the-envelope calculations I did a while back, I’d think your new bowsprit is anywhere from five to ten times stiffer than Douglas Fir and can probably withstand a load at least five times greater before yield or fracture”. This was good to hear from an engineer.  

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