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Thread: Bow beam for 50 foot cat

  1. #1
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    Default Bow beam for 50 foot cat

    Hi all, I have a question regards aluminum bow beams.

    How much do aluminum bow beams weigh "all up"; including A-frame and cable and chainplate on a mid 40's to 50 foot boat?

    Thanks.
    Paul.

  2. #2

    Default Re: Bow beam for 50 foot cat

    Quote Originally Posted by quickcat49 View Post
    Hi all, I have a question regards aluminum bow beams.

    How much do aluminum bow beams weigh "all up"; including A-frame and cable and chainplate on a mid 40's to 50 foot boat?

    Thanks.
    Paul.
    Not sure exactly but should be pretty easy to guestimate; length of pipe (150mm x 4mm about 5kg/m) or mast section add a bit (say 20%) for the A-frame (ends, welds etc), then 12mm SS wire and a bottle screw and some shackles. The wire and the bottle screw is pretty heavy. My guess 50-60kg.

  3. #3
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    Default Re: Bow beam for 50 foot cat

    Thanks, that's about what I figured, but without any direct experience, I thought it would be best to ask.
    Paul.

  4. #4

    Default Re: Bow beam for 50 foot cat

    Quote Originally Posted by quickcat49 View Post
    Thanks, that's about what I figured, but without any direct experience, I thought it would be best to ask.
    Paul.
    Don't forget to allow for the chain plates (anchor points) and all the nuts bolts washers inside that nobody sees. Got to be 5-6kg per side.

  5. #5
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    Default Re: Bow beam for 50 foot cat

    Yes, good point. I hadn't thought of that.

    Thank you Peter. I'll add another 10kg to my estimate.

    Paul.

  6. #6

    Default Re: Bow beam for 50 foot cat

    For the bridle anchor points I welded in some aluminium tangs. Made them oversize, so they can't pull through, fitted them from the inside, then welded them in. Not much weight in them really.

    I glassed the beam into the boat. Solid as a rock. Probably a couple of kilo's per side.

  7. #7
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    Default Re: Bow beam for 50 foot cat

    Yes, I like the glassing idea. It's how we'll be installing ours.

    The main reason for this thread is that we had our designer draw us a carbon fiber cross beam, and I'm not happy with it's finished mass. I therefore wanted to compare it to "normal" cross beams, to better understand my situation, and how to deal with it.

    I asked for a cross beam to be designed without an "A" frame. As found on Manta, Freydis, etc...But my designer wasn't comfortable with having the beam glassed into the boat unless the beam actually acted like a main beam, meaning that it prevents any independent bow movements. Which also means it "weighs" much more than what I expected, and "weight" in the bows is always a bad thing. My beam's mass is more than twice what seems to be the "norm" for a boat our size.

    Granted, getting rid of the "A" frame, which was my choice, is bound to add more mass.

    Due to the beam's mass, we've eliminated our planned longeron, which will save us about 25 Kilos.

    You makes your choice, and you pays your price. My price is going to be a few extra Kilos at the bow. We're leaving the hulls, forward of the heads, empty, no storage, or access hatches on deck. That's 3 metres of empty hulls, which will help. But there's still an oversized anchor, roller furling, forestay, and a 35 m2 jib, all near the ends of the hulls.

    Thanks very much for all of your responses, they've been helpful in sorting out how much of a problem I may/may not, have with trim and hobby horsing.

    Cheers.
    Paul.
    Last edited by quickcat49; 20th January 2016 at 11:29 PM. Reason: I'm all muddled

  8. #8

    Default Re: Bow beam for 50 foot cat

    Quote Originally Posted by quickcat49 View Post
    Yes, I like the glassing idea. It's how we'll be installing ours.

    The main reason for this thread is that we had our designer draw us a carbon fiber cross beam, and I'm not happy with it's finished mass. I therefore wanted to compare it to "normal" cross beams, to better understand my situation, and how to deal with it.

    I asked for a cross beam to be designed without an "A" frame. As found on Manta, Freydis, etc...But my designer wasn't comfortable with having the beam glassed into the boat unless the beam actually acted like a main beam, meaning that it prevents any independent bow movements. Which also means it "weighs" much more than what I expected, and "weight" in the bows is always a bad thing. My beam's mass is more than twice what seems to be the "norm" for a boat our size.

    Granted, getting rid of the "A" frame, which was my choice, is bound to add more mass.

    Due to the beam's mass, we've eliminated our planned longeron, which will save us about 25 Kilos.

    You makes your choice, and you pays your price. My price is going to be a few extra Kilos at the bow. We're leaving the hulls, forward of the heads, empty, no storage, or access hatches on deck. That's 3 metres of empty hulls, which will help. But there's still an oversized anchor, roller furling, forestay, and a 35 m2 jib, all near the ends of the hulls.

    Thanks very much for all of your responses, they've been helpful in sorting out how much of a problem I may/may not, have with trim and hobby horsing.

    Cheers.
    Paul.
    People are often surprised that carbon is not always the lightest. I had to replace my aluminium boom and costed and "weighted" a carbon one. This was considerably heavier than an aluminium boom with rack. Although, a carbon mast is typically lighter so in practice there is a lower size limit for when carbon components become beneficial from the weight point of view.

    Unless you boat was designed to be very stiff, rigidly bonding the forward beam could result it fatigue at the connections. Limiting the beam to resist the upward forces of the fore stay and pin jointing the end connections will be lighter and more reliable long term.

    Regarding your other issues we took the same approach empty forward sections with no deck access. We also mounted our anchor so that it launches from the apron, through the trampoline, rather than over the forward cross beam. This has it compromises but if planned out properly works well and brings the weight of the anchor (and the chain - 3m) closer to the centre of the boat.

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    Default Re: Bow beam for 50 foot cat

    Hi Peter. Thanks for your thoughts.

    I'm surprised to hear of the carbon boom being heavier than an aluminum one. Thanks for that information.

    I understood about there being movement in the bows, but having seen so many home built boats with solid crossbeam connections, I figured mine should be the same, without needing an "overbuilt beam". I've seen Schionnings, Farrier's and Orams, all with solid connections. Although these all have "A" frames, which may also make some kind of difference.

    Having said that, most of these boats also seem to have shorter "unsupported" length in the bows, than our boat. What I mean is that their tramps are not as long as ours are. (3.9m from the back of the crossbeam to the bridgedeck). Which may also explain things.

    I also understand my designer's point of view; which would be that he certainly wouldn't want a failure on his record. I'm guessing this was the deciding factor for the added "robustness" of our beam.

    I'm still disappointed in the "weight" of the beam, but I'll live with it.

    In regards to your anchor placement, and method of launching the anchor, without damaging the bows. Would you mind telling me more about your methods? Either here in this thread, or a PM or e-mail? Would you have a photo, you'd be willing to share, of the anchor placement?

    My thoughts were, if we put the anchor at the back of the tramp, to run a line fwd and over the cross beam, to bring the anchor forward before dropping it into the water. We'd have a roller at the end of the line, for the anchor rode, and "capture" the line at the bow so it doesn't move athwartships, allowing the anchor to damage the bows. Like having a temporary, or movable, anchor roller.

    Retrieval would be the reverse. Pull up the anchor, let out the line holding the roller, and stow the anchor at the aft end of the tramp.

    This would also aid in attaching the snubber, as the rode would be up near the crossbeam.

    In theory; theory and practice are the same. In practice, they are quite different.

    Cheers.
    Paul.

  10. #10
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    Default Re: Bow beam for 50 foot cat

    Hi Paul,

    Paul,
    I have an Erik Lerouge Azuli with a molded front beam, yes it weighs more than an aluminum one but stiffens up the whole boat. Mine is nearly 30 years old and I still need a wedge under one end of one of the keels to stop it rocking on three points when craned out for winter.

    I also store and handle my anchor from the mast beam through a aperture in the forward tramp, the weight of the anchor, chain and multiplat rode as well as the anchor windlass is all centered close to the radius of gyration and I don't need to handle the 20kg anchor and attached chain. When anchoring I just lower straight down below the beam, drift back and when you have laid out sufficient scope attach the bridle with a rolling hitch. I used to deploy the bridle over the front beam as I entered the anchorage, it had a small donut shaped float on it and would be swept back under the anchor to be picked up with a boathook. A year ago I fitted a prodder and now I have a permanent 8mm single braid Dyneema bridle attached to the water stay anchorages, I should have thought of it years ago.

    Hope that helps.

    Peter.

  11. #11

    Default Re: Bow beam for 50 foot cat

    Doing without an A-frame will certainly result in a heavier beam being needed. The A-frame converts the upward pull of the forestay from a bending load into a compression load. Compression is easier to deal with.

    Why the desire to have no A-frame? They're pretty useful, apart from being structurally sound. The A-frame and bridle make a quite effective lifeline around the furler, where you might need one. You can set up furling line guides on the bridle wire. Also, you can set the A-frame up with the forestay fitting plate on it, so all the forestay loads are contained in a neat triangle.

    Also, the trend to build stylish "bent' forebeams adds weight. Again, it's easier to deal with the loads with a straight beam.

    In terms of weight savings, carbon fibre is a pretty expensive way to do it. Someone asked me why I didn't have carbon fibre chainplates, instead of fibreglass. I pointed out that the weight saving would have been less than one kilogramme.

  12. #12
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    Default Re: Bow beam for 50 foot cat

    Hi Peter Lillywhite, nice to hear from you. Talk about comparing apples to apples! I'm encouraged by your post, regards your beam, and anchor setup. I'm not sure what kind of Catamaran the other Peter sails, but he also has the anchor at the mast beam. It's good to hear from you both regards this setup.

    Peter. Do you not have problems with the boat turning side to the wind while drifting back on your anchor? This is what I foresaw as being my biggest problem with the anchor "mid boat". That the boat would turn to the side, and the chain would run along the bottom of the hulls. That, and attaching the bridle.

    It's also nice to hear your boat is so stiff, especially after 30 years. The extra stiffness in the boat is something I had not considered.

    Your post certainly helps me feel better regards my decision to build a beam without the A-frame.

    Thanks.
    Paul.
    Last edited by quickcat49; 21st January 2016 at 10:17 PM.

  13. #13
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    Default Re: Bow beam for 50 foot cat

    Hi 44C, thanks for your post.

    One of my main reasons for contemplating building my own carbon beam was that I have two rolls of carbon fiber here that I wanted to use, and the cost of a beam from Selden is near $9000 Cdn (with the sudden dive of the Canadian dollar). Building my own beam with carbon already on hand will cost less than a thousand dollars worth of epoxy, mould making material and infusion material. The beam is also good practice for building our infused carbon mast.
    I thought if I was building my own beam, I'd like something different, so we decided on a beam without the "A-frame".

    I like your idea of using an aluminum beam, but I didn't want a round crossbeam, and trying to find oval aluminum extrusions, in my country, was driving me crazy. A bare mast was also not easy to find. So building the beam myself seemed to be the least stressful of the options at hand.

    As an aside; our chainplates are also composite, fiberglass, like yours. Even though carbon fiber is much stronger than glass in resisting bending forces, there isn't much difference in it's resistance to the forces exerted on a chainplate. So, as I understand it, to build chainplates out of Carbon fiber is of little benefit.

    Thanks again for posting your ideas.
    Paul.

    I may have posted this photo elsewhere, but this is the front part of the beam, the aft bulkhead will be built this spring. No room in the house at the moment, it's full of other boat stuff. I have a patient wife.
    Paul.
    Attached Images Attached Images
    Last edited by quickcat49; 21st January 2016 at 10:23 PM.

  14. #14

    Default Re: Bow beam for 50 foot cat

    Not trying to influence you one way or the other, but yes, buying a ready made aluminium beam is ridiculously expensive. However, you can build your own very cheaply.

    Most rigging companies will sell you lengths of bare mast section, as well as spreader section. Even a large boom section might be suitable.

    The company we bought from simply charged us by the kilo. From memory, the materials for my forebeam cost just a few hundred dollars, all up.

    One thing that swayed me towards aluminium was the consideration of possible collision damage. ie.let's say a boat drags down on to you, hits your forebeam. There's a lot of noise, but visibly, only some cracks in the paint. Is your forebeam structurally OK?

    With an ally one, it would be pretty easy to tell.

  15. #15
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    Default Re: Bow beam for 50 foot cat

    44C.

    Finding a suitable extrusion here was a frustrating, and fruitless, experience. I've since found a place, but my beam is already well on it's way to being finished.

    I agree with your thoughts on collision damage, it's something I'll worry about in a bad anchorage. But even though carbon is not the best material for resisting impact loads, it isn't crystal either. Your point is valid, and one I considered.

    Having said that, my wife made a good point on the subject. While I was fretting about impact damage, she asked how often I've heard of a cat getting impacted at the crossbeam. I'd only heard of one, who ran into a buoy at full clip.

    With the prodder in place, hopefully the guy wires will push the offending boat (or buoy) to the bows, in lieu of hitting the beam... who knows. I hope to avoid these problems by anchoring in shallow water, where most heavy boats can't drag before going aground.
    We draw slightly more than you, at about 540 mm fully loaded, and about 400 mm lightship. At least that's what the designer says.

    Cheers, and stay well.
    Paul.

  16. #16
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    Default Re: Bow beam for 50 foot cat

    Peter. Do you not have problems with the boat turning side to the wind while drifting back on your anchor?



    I do fall of and drift sideways when anchoring but don't see it as a problem. I have 20m of 8mm chain attached to 65m of octoplait rope, and usually anchor in an area with a 5m range. As long as the rode is paid out in sympathy with the drift rate it doesn't come near the hulls, once I've reached the desired scope I cleat the anchor rode and load up the anchor to dig it in. This is a gentle process as before the rope rode can come near the hulls it has to straighten the rode and lift the chain which acts as a shock absorber. When recovering the anchor the rode can reach the hulls, its just necessary to be patient in the use of my anchor winch. In strong winds I tend to use the outboards (I usually anchor under sail) to drive up wind of the anchor to take the load of the anchor windlass.

    Peter.

  17. #17

    Default Re: Bow beam for 50 foot cat

    Quote Originally Posted by peter-lillywhite View Post
    Peter. Do you not have problems with the boat turning side to the wind while drifting back on your anchor?



    I do fall of and drift sideways when anchoring but don't see it as a problem. I have 20m of 8mm chain attached to 65m of octoplait rope, and usually anchor in an area with a 5m range. As long as the rode is paid out in sympathy with the drift rate it doesn't come near the hulls, once I've reached the desired scope I cleat the anchor rode and load up the anchor to dig it in. This is a gentle process as before the rope rode can come near the hulls it has to straighten the rode and lift the chain which acts as a shock absorber. When recovering the anchor the rode can reach the hulls, its just necessary to be patient in the use of my anchor winch. In strong winds I tend to use the outboards (I usually anchor under sail) to drive up wind of the anchor to take the load of the anchor windlass.

    Peter.
    I think 2 Peters caused some confusion here. But I concur with the other Peter. Not really any problems. I anticipate that it would be more of a problem with mini keels, we have daggerboard as well.

    With 2 engines it is not difficult to control the angle of the boat and having the anchor central is much easier to work from if you do get stuck. We once snagged on an old trawl (boards and all) lifting it using the wave action took a long time and would have put enormous strain on a fore beam. Also leaning down through the tramp to cut it away was far easier than if we had had to hang over the front. Once the anchor is down and dug in the load is taken on the bridle so is no different than anchoring over the fore beam.

  18. #18
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    Default Re: Bow beam for 50 foot cat

    Thanks Peter, um, both Peters.

    It seems like you both have similar setups, and similar experiences. Neither of you have problems with the anchor at the mast beam. So I guess I don't have to fret about it. That's one more item I can cross off my list of worries.


    Thank you both.
    Paul.

  19. #19
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    Default Re: Bow beam for 50 foot cat

    Have you thought about the bridal lines interacting with the prodder stays? The best option is to have the prodder stays very far forward and higher up, with the bridal points further back, which it seems you can do since you said you have long bows with the beam further back. With this setup the bridal will be under the prodder stays will not hit the prodder stays even if you sail over the anchor or are bow and stern anchored in cross current/wind.

    I just fitted a prodder and its a fouling problem, but with good design from the start it should not be an issue. After looking at many prodders VS anchor bridals on cats it seems most setups are poor.

    This is a sister ship to my boat. They just made a ridiculously short bridal so it would go under the stays. Not ideal. With longer bows and a higher mounting points for the stays the bridal could be a decent length. Many others put the bridal over the stays which gives the chafe issue in some situations.




    Interesting project you are doing. Are you able to share more about the boat and designer?
    Last edited by dennisail; 3rd February 2016 at 12:07 AM.

  20. #20
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    Default Re: Bow beam for 50 foot cat

    Ah, nice idea. I've considered that there might be interference, but wasn't clear where or how. I see how a high prodder, which would bring the stays up, could help to prevent that sort of interference. We're pretty sure we'll wait and use the boat for a while before installing a prodder. I will, however, be building a place for it to attach to the crossbeam, before we install the beam.

    Thank you.

    The boat is a Kurt Hughes 45. We had Kurt do some modifications for us, including the "frameless" bow beam, shorter bridgedeck, shorter mast beam, and longer hulls. The boat is now 15m long and the bridgedeck is only 6m long. Compared to the original design of 13.7m hulls and 7.5m long bridgedeck. Also changed is that the boat is now setup with inside steering, rather large windows, and forward "workpit" for mast work.

    Cheers.
    Paul.


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