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Boat Forum / Building / October 2005how do I make a bowsprit?
Hello, I'd like to add a 4' bowsprit to an IP23 sailboat. To what extent does the bowsprit rely on the rigging for it's strength vs it's actual strength of materials? I was hoping to use a one inch thick piece of epai 6 feet long, two feet on deck, four feet for the bowsprit and 2 more 4' long, one inch thick planks butting the bowstem all laminated/screwed together. About 3 1/2 inches wide with two side stays and a 5/8" stainless rod for the dolphin catcher and a stay to the masthead. I'm looking for some advice as to whether this is too much or too little. Is there a better place to ask this question or get some information? Thanks for your time. Not a simple calculation. Note that the loads go in all directions; up when at rest, but down when you've buried it in a wave and athwartship when your jib is pulling on a broad reach. Do you have a forestay on your mast? Are you going to keep it? If not, how are you going to transfer the load back to the hull. That forestay is (arguably) the hardest working line on the boat. Classically, the heel is buried in heavy timbers, the "partners" (knight heads) at the bow pick up the side loads, and the gammoning holds it down. The latter is aided by stays down to the hull. I'd suggest that 1" siding is too little. You might see if Dave Gerr has anything to say about bowsprits in his "Nature of Boats." It's also normal to make provision for unstepping the bowsprit since it gets damaged easily and the boat fits into storage spaces better without it. (I'm not sure what you have in mind when you say "all laminated and screwed together.") Roger derbyrm@NOSPAMearthlinkNOSPAM.net http://home.earthlink.net/~derbyrm > Hello, I'd like to add a 4' bowsprit to an IP23 sailboat. To what > extent does the bowsprit rely on the rigging for it's strength vs it's [quoted text clipped - 6 lines] > much or too little. Is there a better place to ask this question or > get some information? Thanks for your time. >Not a simple calculation. Note that the loads go in all directions; up when >at rest, but down when you've buried it in a wave and athwartship when your [quoted text clipped - 3 lines] >are you going to transfer the load back to the hull. That forestay is >(arguably) the hardest working line on the boat. Yes, I'm going to keep the existing forsail and stay as is so I will have to figure out how to add another stay to the masthead. There is also an existing cutter stay mid foredeck. I'm thinking along the lines of some early Lyle Hess traditional looking boats with a small yankee cut sail up high on the bowsprit so it clears the pulpit and bow when whipping about. The rig is down now and decked in the yard where I can work on it anytime. >Classically, the heel is buried in heavy timbers, the "partners" (knight >heads) at the bow pick up the side loads, and the gammoning holds it down. >The latter is aided by stays down to the hull. I'd suggest that 1" siding >is too little. You might see if Dave Gerr has anything to say about >bowsprits in his "Nature of Boats." Yes, I did notice this when taking my reconasance walk at the local dock. Unfortunately all the boats I saw were 40'+ heavily built Hans Christen clones but I do see the tendency to incorperate the heel into the deck and bow structure. I couldn't find any small boats. One mid sized wooden boat had a tiny round pine pole which looked like it could be shipped and seemed to rely on the rigging for it's strength. >It's also normal to make provision for unstepping the bowsprit since it gets >damaged easily and the boat fits into storage spaces better without it. >(I'm not sure what you have in mind when you say "all laminated and screwed >together.") The boats I saw looked like super permanant installations. It did occur to me pitch poling or ramming a piling would wreck the whole front of the boat and probably bring the mast down unless the arrangement was mechanically fused somehow or tremendously overbuilt. Thanks for your response. >Roger >derbyrm@NOSPAMearthlinkNOSPAM.net [quoted text clipped - 10 lines] >> much or too little. Is there a better place to ask this question or >> get some information? Thanks for your time. I can't speak to bowsprits, but in land based construction the general rule of thumb for cantilevered decks, bay windows, etc. is 2/3 vs 1/3, i.e. the exact opposite of what you propose. 2/3 of your structural member is buried in the existing structure, one third of it is outside, and free to bear weight. In other words, to have a cantilevered 3 ft deck/landing, no posts to the ground, you need to your 2x8s buried by 6 feet. Most timber bowsprits I've seen are as tall/deep as they are thick, round, or a 4x4, 3x3, etc..... Why do you want to do this, anyway? > Hello, I'd like to add a 4' bowsprit to an IP23 sailboat. To what > extent does the bowsprit rely on the rigging for it's strength vs it's [quoted text clipped - 6 lines] > much or too little. Is there a better place to ask this question or > get some information? Thanks for your time.  SignatureI am building my daughter an Argie 10 sailing dinghy, check it out: http://home.comcast.net/~jonsailr >I can't speak to bowsprits, but in land based construction the general >rule of thumb for cantilevered decks, bay windows, etc. is 2/3 vs 1/3, [quoted text clipped - 3 lines] >deck/landing, no posts to the ground, you need to your 2x8s buried by 6 >feet. I'm getting the idea the main support is from the rigging forming various trianges. >Most timber bowsprits I've seen are as tall/deep as they are thick, >round, or a 4x4, 3x3, etc..... Good point. That was my first plan but when I roughed out the pieces out it felt too heavy and looked disproportionate. I could look for lighter wood I guess. >Why do you want to do this, anyway? It turns out IP23's are notoriously bad sailors and there is a commonly perceived need among owners to move the sail effort forward in an attempt to make the boat come about and perform with any kind of success upwind. They were offered in various stages of completion and were not designed specifically as sailboat. Thanks. >> Hello, I'd like to add a 4' bowsprit to an IP23 sailboat. To what >> extent does the bowsprit rely on the rigging for it's strength vs it's [quoted text clipped - 6 lines] >> much or too little. Is there a better place to ask this question or >> get some information? Thanks for your time. Good luck with your plan for the bowsprit. My only comment is that a wire with a user installed lower fitting is much superior to a rod for the bobstay. Sooner or later, everyone rams a float or something. A rod will stay bent; wire goes back to its original straightness all by itself. Corrosion at the lower end is often a problem because of the cycling in and out of the water. By using user installed fittings, the cold working of swaging is avoided and corrosion greatly limited. A great many designs would benefit from having a bowsprit. It reduces weather helm and is a perfect place for storing the anchor in the ready position. I'm not a purist and recognize that terminology varies with region and country, however, I could suggest a couple correction in "Bowsprit Nomenclature" use here. 1. The rod or wire you describe, going from the end of the bowsprit, down to the stem of the boat is called a "Bobstay" and if you have a strut in the middle to improve the load geometry, that is called a "Dolphin Striker". The fitting or attachment where the Bobstay is attached to the stem is call a "Stem Band". 2. The wires or chains the goes from the end of the bowsprit to the side of the hull are called "Whisker Stays". My intentions are not to be 'anal' but to try to preserve the nautical terminology when ever I have the opportunity. Just constructive "clarification". SignatureMy experience and opinion, FWIW -- Steve s/v Good Intentions > Hello, I'd like to add a 4' bowsprit to an IP23 sailboat. To what > extent does the bowsprit rely on the rigging for it's strength vs it's [quoted text clipped - 6 lines] > much or too little. Is there a better place to ask this question or > get some information? Thanks for your time. >I'm not a purist and recognize that terminology varies with region and >country, however, I could suggest a couple correction in "Bowsprit [quoted text clipped - 12 lines] >terminology when ever I have the opportunity. Just constructive >"clarification". Nicely put, thank you Steve. Thanks for the right terminology. Can the same terminology be used for a sternsprit. I do not no much about bowsprits. I have seeing some made with wood and other with 2 " pipe. I often wonder what are the advantages and drawback of having a bowsprit. > >I'm not a purist and recognize that terminology varies with region and > >country, however, I could suggest a couple correction in "Bowsprit [quoted text clipped - 14 lines] > > Nicely put, thank you Steve. A "bowsprit on the stern" is called a boomkin. Usually, they are wishbone shaped when viewed from the top; two members that meet. I have had bowsprits on most of my dozen sailboats over the past 45yrs on the water. The main advantage is increasing the overall length, with respect to carrying more sail or more head sail combinations. I don't like to see it as a advantage for getting the anchor off the bow. I much prefer to have my anchor roller at the stem head since a roller on the end of the bowsprit puts too much load on the headstay and much too much noise when the boat is hobby horsing at anchor. Here are a couple of pictures of my present arrangement that allows me to have two bow anchors, on chain, lead to a single anchor windlass. http://www.hctc.com/~esteve/INGRID%20PICs/dogonbw1.jpg http://www.hctc.com/~esteve/INGRID%20PICs/dogonbow.jpg (the dog "Shipmate" is no longer part of the crew) The bowsprit is made of 2" SS pipe with aluminum deck plating. There are cut outs for the anchors to come thru. I'm very happy with the whole system. Note that this type of bowsprit/platform eliminates the need for Whisker Stays. The Bob Stay (not pictured) is 5/8" rod. I've run into the dock and a buoy, at slow speed and it hasn't bent (yet). The stem band is 3/4" X 1 1/4" X 4' and runs down the stem and is through bolted with a similar backing plate at each bolt. SignatureMy experience and opinion, FWIW -- Steve s/v Good Intentions > I do not no much about bowsprits. I have seeing some made with wood and > other with 2 " pipe. Take a look at these photos from the Pacific Seacraft Dana 24. Perhaps similar in size / layout to the IP23...? Here's the 'sprit + rig: http://www.pacificseacraft.com/cgi-bin/printview.php?2422 and here's how to buy the 'sprit: http://www.pacificseacraft.com/parts/notes.php?sc=2473129&cat=bowsprit Good Luck. MW |
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