The first indication there was a problem with the bowsprit on my 50-foot schooner was when I was hoisted up the foremast using the electric windlass bolted on top of the bowsprit. The operator mentioned the windlass “moved” as he hoisted me using 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 long threaded rods securing the machine through the foredeck and they were all nicely tight.
Back on deck it didn’t take five minutes probing with a screwdriver to realize there was some seriously rotten wood beneath the windlass. Before long I had the windlass removed, that brought more soft wood out with the four long threaded rods. Further scouring with a chisel revealed extensive rot in the nearly 10-foot long bowsprit. I scoured more and more soft wood from the interior of the spar, then gave up after a length of 38-inches!
Britannia’s bowsprit was a tapered lamination of nine sections of timber glued together. It measured nine feet six inches long, 8-inches square at the heel and 5-inches square at the crance iron. I hoped it would be possible to repair the ‘sprit in-situ by scarfing some new planks in, to replace the damaged ones. That idea was unfortunately ruled out as it became clear that poor old Britannia needed a completely new bowsprit.
The previous owner’s log showed a new bowsprit was installed in February 2005 which didn’t persuade me much towards a third one in wood. But if I was to make it in anything else it had to be the same shape and at least as strong as the previous one.
When considering bowsprit strength there are a number of factors to consider. When under sail there is an upwards pull on the ‘sprit which varies depending on the point of sailing, the wind strength and of course the size of the head sail(s). This upward pressure is resisted by a number of things, mainly the bobstay and in Bitannia’s case, also a dolphin striker that transmits some load into the bow, the bowsprit shrouds, and the actual strength of the ‘sprit itself and how it is secured to the deck. If all fittings are correctly tensioned the opposing forces result in a mainly compression force on the bowsprit, pushing it backwards.
These interactions would be fairly easy to calculate in a simple static force diagram. However, a sailboat is hardly static and a major unknown factor is when the bow ‘scends’ into a head sea, plunging the complete pulpit and even the bow into solid water. This imposes goodness knows what loads on the structure and nobody, including a sailboat architect, could tell me what these extra loads might be. A friend loaned me Skene’s elements of yacht design that has a small section on bobstays but surprisingly nothing about bowsprits, but it does include this 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 of error and it seemed in the final analysis it was all based on experience and perhaps destruction tests, none of which was helpful to me.
ALTERNATIVES AND ESTIMATES:
I took photographs of the bowsprit and also a drawing 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 and then came the next shocks! One price 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 where Britannia was in Florida. Also, no actual time for completion was given by either builder even though I specifically asked for it so that I could plan the operation. It was obvious none of these people really wanted this job.
With these people out of the picture, my next option was to see if I could buy the wood somewhere and build a new bowsprit myself. I located a lumber supplier in Minnesota, who quoted $830.00 for four 2” inch thick finished straight grained planks of Douglas Fir, 10-feet long and 8-inches wide.
Building the ‘sprit myself would be the cheapest way, but a daunting task. First, these large planks would need clamping and glueing together, then the massive billet—over 200Llbs and about as big as a railroad tie—would need shaping into a taper with a 4- inch perfectly round section on the end to carry the crance iron. Additionally, all this would have to be done with hand tools, in my garage because I had no actual workshop
Over the years I have done some very big major projects on Britannia including changing the complete rig from a ketch to a schooner and inventing and making a square sail on the foremast, but this whopping great bowsprit was just too much for me to comprehend at that time. I decided to explore the possibility of having the thing fabricated in aluminum. At least it wouldn’t go rotten for a third time and would likely be a bit lighter.
I have some structural design training, but even luckier for me my son-in-law Jim is a qualified patent engineer and offered advice on an aluminum design. After researching different types of aluminum I decided to specify ¼-inch thick type 6061 structural aluminum plate. This is as hard-as-nails and much stronger than regular aluminum. Drilling it is like drilling stainless steel.
The new ‘sprit needed to be the same shape and size as the existing spar, so that everything 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 eye-beam that is well known for stiffness in both bending and compression
Two aluminum fabricating companies gave me estimates. One was $1525.00 including powder-coating both the bowsprit and the crance iron. The other was $2200.00 in raw unpainted aluminum. It won’t be difficult for boat owners to guess which was the ‘marine fabricator’s’ quote, as opposed to a regular welding company near Orlando, Florida.
I was also interested in trying to work out the weight of an aluminum sprit against the existing wooden one. I guessed the existing spar was made of something like Douglas Fir that weighs roughly 35L bs per cubic foot. I measured then calculated the whole bowsprit to be 3.24 cu ft., which made it about 113Llbs. The weight of 1/4-inch 6061 aluminum sheet is 3.56Llbs per square foot. I calculated the square footage of each piece in the assembly that all added up to 27.10 sq ft., including a round tube at the head to carry the crance iron. This gave a weight of about 100Llbs.
I therefore decided to have the bowsprit made in aluminum and I gave the job to a welding firm in St Cloud, near Orlando. They had done work for me before and I knew the excellent quality of their welding. Another advantage was that they carried the aluminum in stock and could start the job almost immediately.
CONSTRUCTION.
After all the pieces had been sheared out of a 10-foot x 4-foot sheet, the top and bottom sections were welded to the center spine. The bottom was tapered slightly to form the underneath towards the tip. A new staysail bracket was also welded through a slot in the top plate. The original bracket was bolted through the deck thus avoided two more potential leaks. The two sides were then welded to the top and bottom to complete the box and a 4-inch diameter tube was welded on the tip to carry the crance iron. I asked for the heel plate to be screwed on the end of the bowsprit, so I could bolt it to the two samson posts (bitts) from inside. I also drilled two holes in the bottom, to drain any water which might find it’s way into the interior. Heel plate The whole design resulted in a very stiff spa
INSTALLING THE NEW ‘SPRIT.
The damaged bowsprit was still in place and in order to remove it I supported the pulpit and grating with halyards from the foremast that saved unbolting those cumbersome items from each other. Next I unbolted all the fasteners holding the grating to the bowsprit and deck, then with a few willing helpers the damaged bowsprit was levered clear from the bow.
The ‘sprit weighed 116Lbs., so allowing for the missing rotten wood I was only about 3Lbs out with that calculation. I filled all the holes in the deck then primed and repainted the area. Britannia looked very forlorn without her majestic bowsprit which is the essence of the clipper bow.
When everything was ready the new bowsprit was manhandled into position and carefully lined up with the gratings and samson posts. The long threaded rods that hold the windlass pass straight through the bowsprit into the chain locker below and help secure the ‘sprit to the deck. Holes were then piloted though the samson posts and the ‘sprit bolted to the posts from inside the tube. Holes were then piloted through the bowsprit and the gratings bolted in place, using the original stainless threaded rods.
The two large bronze anchor rollers never revolved properly since I had the boat and the chain and anchor chafed against them. Before fitting them back I reamed the 1/2-inch holes clean then drilled and tapped an oil hole into the center of each roller. Oil could then be poured in periodically to keep the rollers revolving smoothy and I screwed grub-screw into the holes to keep water out.
I had sanded the two gratings, and three coats of varnish restored them like new. I had to make fourteen 1-inch, and six 1¼-inch teak plugs to cover the holes in the gratings and samson posts, all made by hand because I didn’t have plug cutters for those sizes. All joins in the ‘sprit and deck were caulked liberally with 3M 5000. The crance iron, which had been powder coated white, was then pushed on its tube and the jib stay, forestay, bobstay and shrouds relocated and tensioned.
The new bowsprit looked magnificent in its dark blue livery, matching the rest of the spars and topside stripe. It arrived exactly two weeks from placing the order and weighed 96Llbs—I was 4Llbs out in my calculation!
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 her on the hard because we didn’t need scaffolding or ladders as we would have needed on land, and we could also continue to live aboard. The reassembly operation took three days, during which the spit was removed and replaced for bedding adjustments seven times
I now wondered how we might test the strength and rigidity of the new structure. Of course, the ultimate test would be at sea in heavy weather, but I also decided to perform a simple static test by bowsing down the bowsprit to the dock to see what would happen. I disconnected the jib and staysail forestays, then with only the bobstay and shrouds attached I hooked the anchor under the dock directly below the bowsprit. Then I tensioned the chain with the windlass which I was pleased to see never budged. This pulled the bow downwards and the bobstay bracket disappeared under water. A second touch on the windlass button hauled the bow down further and the chain was now bar tight. Amazingly, the bobstay also remained taught—which would have gone slack if there had been any deflection in the ‘sprit and the bow. Bowsprit test. At this point I heard ominous creaking noises from the dock timbers, so I quickly slacked the chain off. I didn’t want the be accused of breaking the dock, even though everyone knew many of the beams were rotten from old age. Hauling a heavy displacement boat down like this imposed some impressive loads on the bowsprit but there was absolutely no evidence of and settling or shifting, or paint cracking anywhere along the new bowsprit.
On seeing the finished result Jim wrote, “Based on the back-of-the-envelope calculations I did, and the way it’s been built and tested it, I think your new bowsprit is anywhere from five to ten times stiffer than a wooden job, and can probably withstand a load at least five times greater before yield or fracture”. This was good to hear from an experienced design engineer, but I hope old Neptune doesn’t have other ideas the first time we hit some heavy weather.