Need sugestions on building a bow sprit for a Bristol29

[ddsailor25]

I would like to build a bow sprit for my bristol 29. If someone has done this project on a simular boat I would be intersted in how you did it. I assume you have to remove the original harware and rebuild and glass in the area. I don't plan on moving the head stay location and im wondering if a solid bob stay will be necessary. Basically, this bow sprit is going to be used for anchoring and will have a bow roller built into it. Any sugesstions would be greatly appriciated.

Dave

Bristol 29
Pride-N-Joy

[Triton106]

Dave,

If you are only going to use the bowsprit as anchoring platform I don't think you can find a finer example than Tim's setup. If, however, you are going use it to move forestay further out to reduce weatherhelm you can find a really well documented example of another Bristol 29. Here are the links.

http://www.triton381.com/projects/resto ... atform.htm
http://www.bristol29.com/Projects/bowspirt/bowsprit.htm

I will be very interested in this discussion as I am planning to add a bowsprit to my Triton.

Good Luck.

[Hirilondë]

I have done several bow roller installations on sailboats. I have always done something similar to what Tim did. There is no reason at all to alter the standing rigging of the boat. You are merely fabricating a platform for the anchor roller. The anchor will have to be off-center anyway. Whether you build an off-center platform, or one like Tim's with just the roller hardware off-center is a matter of aesthetics. The bobstay is used to carry the load of the headstay to the hull. So you don't need one for your anchor platform.

[Rachel]

For those of you who have built/used this type of platform, I have a question.

Backtracking, I've found anchor platforms to be really handy, but the ones I've used have all been on cutters where there was a bowsprit that was reinforced by a headstay/bobstay/whiskerstays as part of the rigging.

Liking the function, I've thought it would be nice to have one myself, but without the rigging to reinforce them, in my mind I can't see what keeps them from just breaking off if you're anchored and the boat fetches up or veers. I realized that you'd have a snubber line, but I still wonder about it. But then, I've never had one of this type, so I haven't seen one in action.

Rachel

[Hirilondë]

Liking the function, I've thought it would be nice to have one myself, but without the rigging to reinforce them, in my mind I can't see what keeps them from just breaking off if you're anchored and the boat fetches up or veers.

Hmmm, fetches up or veers? Winds veer, they also back. A veering wind is changing in a clockwise direction and a backing wind in a counter- clockwise one. The boat swings with the wind unless the current is stronger. I'm not sure what you mean by fetches up.

You will note in Tim's pictures that his platform is bolted through the deck with 6 bolts. This will off-set any force down on the end of the platform, especially the after most bolts which create a greater lever arm than the overhang. They would off-set just about any force up, but I can't think of any time there would be such a force. They would off-set any twisting forces caused by the boat swinging as the pattern is spread out which is a greater lever arm than the overhang. All a bobstay really does is keep the bow sprit from being levered up which is what the fore stay is trying to do. It doesn't do much if anything to off-set any forces of the anchor rode which are down or sideways.

The most important design considerations for an anchor roller platform are a somewhat massive strong piece of wood, enough lap on the foredeck to achieve a 2:1 or better ratio of overlap to overhang and a layout for the roller that allows for storage of the anchor and ease in the pay off of the rode. You need enough overhang to raise and lower the anchor without it hitting your hull, but no more than necessary as the added leverage increases forces on everything involved.

I don't know it this helps explain anything regarding your questions Rachel.

[Rachel]

Hmmm, fetches up or veers? Winds veer, they also back. A veering wind is changing in a clockwise direction and a backing wind in a counter- clockwise one. The boat swings with the wind unless the current is stronger. I'm not sure what you mean by fetches up.

Sorry if I used those words incorrectly. In my mind "fetches up" was describing when there is a swell coming into the anchorage, and the boat "bounces" up and down, and at the "up" point in the cycle the boat tightens the rode. In other words there is some shock loading when the snubber (or potentially the rode) go tight at just the "right" point in the swell's going under the boat.

When I said "veers," I was thinking about how sometimes the boat can hunt a bit back and forth, and thus there can be a side-load on the anchor roller, and also the sprit when it slews off to one side.

If you know the correct terms for those things, I'm always happy to expand my vocabulary.

Thanks,

Rachel

[Rachel]

Replying to myself; is that a bad sign? ;)

Okay, not that online dictionaries are the ultimate source, and I only did a really quick search, but here's what I found on Dictionary.com. I think my use of "fetches up" comes from definition "c."

fetch up,
a. Informal. to arrive or stop.
b. Older Use. to raise (children); bring up: She had to fetch up her younger sisters.
c. Nautical. (of a vessel) to come to a halt, as by lowering an anchor or running aground; bring up.

And for "veer" I would say it was use 4. I was thinking of.

–verb (used with object)
3. to alter the direction or course of; turn.
4. Nautical. to turn (a vessel) away from the wind; wear.

I'd still very much like to know if there is a better or more correct way to say what I was describing.

[Hirilondë]

I have heard of your #3 for veer, but since it isn't a nautical application I discounted it. I would say bear off, head down, or fall off if I meant to head away from the wind. Wear away is a very old seldom used expression, but certainly correct. I have never heard of #4, but not sure that means anything.

If you're really a glutton for punishment you can read veering and backing winds defined

[ddsailor25]

Thanks for the tips. Tim's set up is exactly what I'm looking for. I have to get some measurements and see about removing the existing hardware thats up there, but that shouldn't be that bad of a project. It will give me something to do over the winter time.

Dave
Pride-N-Joy

[Triton106]

Rachel,

I am sure you have read what happened to Tim's first anchor platform. I believe your concern is completely valid. As to the solution, I think you may have read Tim's solution of using 3/8" stainless steel plate to back the mahogany platform on his second anchor platform. If I were to add an anchor only platform that is exactly what I would do, except in my case I would like to move the forestay out a couple of feet. My question (sorry to hijack the thread) is whether stainless steel backing plat would be necessary if I were to add a bob stay (similar to the Cape Dory's) and balance that with the forestay (moved out).

If anyone is interested in Tim's experience here is the link: http://www.triton381.com/projects/small ... damage.htm

Best regards,

[Tim]

Note that the damage to my anchor platform occurred when tied to a mooring during a storm, and not while anchored. The pitching of the boat in large, steep waves, coupled with a protruding anchor, allowed the mooring line to hook on the anchor, forcing it downward, breaking the platform.



I had a near repeat performance a few years later; this time, I'd removed the anchor in anticipation of the storm, but nonetheless the spare mooring line hooked over the top of the platform and caused a similar problem, though with the 3/8" SS plate all it did was bend the plate down a bit.

Again: "all" it did is bend a 3/8" plate that was only cantilevered less than a foot...yeah, no forces involved, nope, none. The bend and other damage is subtle, but it's there. Impressive, really. (I still have the same platform, bend and all.)



The lesson learned is that an anchor platform shouldn't extend very far past the stem--just far enough to allow the anchor to seat nicely without marring the hull or stem casting, as too far an extension can foul mooring lines. Mother Nature always wins.

I was relieved to later move my boat away from this over-exposed mooring place. If I'd stayed there much longer, I would have re-designed the anchor roller platform. Where I keep the boat now, I am not concerned since there is no fetch for seas.

All this being said, I don't see any problem with this sort of arrangement for the typical coastal cruiser as far as anchoring goes; mine has always worked admirably in a (relatively tame) variety of typically-encountered cruising conditions for 8 seasons. But be aware of how the anchor, roller, and platform might interact with any mooring lines you have, as applicable.

[Triton106]

Wow, Tim - that's incredible force to bend the 3/8" stainless steel plate. I have always heard that in those conditions the stainless steel pulpit and anchoring platform can be "twisted like a pretzel" but have never even seen a picture like that. That leads me to question what the bowsprit will look like if it overhangs the bow by 3 feet even if it is stayed with bob and wisker stays. Your experience convince me to build as a strong bowsprit as possible which in my mind would include a solid short spar of 6"x6" and no longer than 3 feet similar to the ones on the Morris Yacht Frances (see picture below). I would also add the anchoring platform on top. In any case, I would still rather have the anchoring platform damaged than the hull.

[Rachel]

That leads me to question what the bowsprit will look like if it overhangs the bow by 3 feet even if it is stayed with bob and wisker stays.

I think it's a whole different ballgame when a sprit is stayed, and that even visually "slender" sprits can be quite strong. That's because, as I understand it, the stayed sprit is loaded in compression, and the main forces are taken by the standing rigging as a system. The rigging keeps the sprit in line so that there aren't other forces on it.

Granted, one still wouldn't probably hang an anchor roller from the very middle of the sprit (it doesn't make sense to do that anyway, just for usability), but I wouldn't necessarily judge a stayed sprit to be weak just because it isn't super beefy.

On the Westsail 32, for example, the bowsprit is a good four feet long, and is not extremely thick; yet, it makes a very sturdy place to mount an anchor roller/snubber. I've anchored many nights with such a set up, and although you always have a weather eye open when you're anchored, the sprit was never a specific concern (it is rigged with forestay, bobstay, and whisker stays).

Rachel

[Triton106]

Thanks Rachel for the insight on the relative strength of stayed bowsprit vs. unstayed anchor platform. I have always liked the Westsail 32 bowsprit for its looks and always felt that it is also well designed (see below - credit goes not the owners of Fluid Motion - isn't that pretty?). I plan to copy the design (albeit not exactly the same dimension as it is obviously too large for the Tritons.) But I note that even then it uses a solid spar of 4"x5" and a pretty beefy platform (1-3/4"). Have you had any issues with the anchor roller set amid the platform vs. at the tip of the platform as in Tim's setup?

[Rachel]

Hi Ray,

First, I don't think the platform part "counts" at all in a structural sense. It looks beefy, but it's really just there to give you a place to stand and doesn't strengthen the system at all. The anchor shanks do kind of rest on it, but they are really being held by the rollers, which are mounted to the sprit.

I didn't have any problems with the anchors mounted as they are shown in the photos; in fact, I can't imagine why one would want them any further forward than necessary. Where they are shown (which is the usual place on a W-32) seems about right to me. Just far enough forward so that they don't interfere with the fiberglass on the stem. Speaking for Tim here, I don't think his anchors were at the end of his platform in order to be at the end of the platform, but rather to be just far enough away from the topsides to not mar the paint/fiberglass. It's just that, being unstayed, his platform was as short as practicable, and so the anchors were at the end of it.

One issue that can crop up in this type of set-up is the anchor chain making a grinding sound as it touches the bobstay (amplified inside the boat). On the W-32 I sailed on, we ran a piece of white sanitation type hose over the bobstay (loose fit), and that kept there from being any noise. (There typically wasn't any strain from it because the chain would hang loosely with the strain taken up by the nylon snubber line.)

That is a pretty looking foredeck in your photos!

Rachel

[ddsailor25]

Now looking at the damage that Tim had I have concerns. We also have to keep our boat in open water and it does get very rough in there. Our problems is that we're about a good hour away from the boat and it's not practical for us to drive there if we're going to get a storm to remove the anchor. I'll have to think about this to see if it's something that I really want to do. I could remove the anchor weekly, but that might get old very quickly.

Dave

[Quetzalsailor]

Yikes! To Tim's damage.

I used to moor Q with a bridle of 3/4" nylon passed through the bight of the mooring pennant(?...waiting for Hirilonde) on the mooring. The pennant was too large to pass through Q's chocks. I affixed each end of the bridle to one of the two big cleats on the foredeck and passed each end through the chock on each side. I never bothered making up a nice neat bridle because I soon observed that Q would hunt on the mooring anyway, despite being moored symmetrically, and each leg of the bridle would 'pop' under the CQR as she swung. This was noisy, but worse, pointed to the inevitability of chafe. Additionally, I fretted about chafe between the bridle and the mooring pennant. I did not wish for the chafe, and I did not wish the marina to be able to blame me for not using their pennant correctly if Q were to get away. I ground the chocks open a bit further.

Several boats in the marina use bridles. One is a Valiant (or clone) with a bowsprit and a bobstay. As it hunts, the bridle drags against the bobstay.

[Hirilondë]

I used to moor Q with a bridle of 3/4" nylon passed through the bight of the mooring pennant(?...waiting for Hirilonde) on the mooring.

LOL, ok, I'll bite. A pennant is a type of flag. A pendant is a type of line.

If an anchor stowed on a roller is in the way of a mooring pendant it really should be moved, or chocks located such that the pendant never touches it. I don't know of any great solution for a bobstay being in the way. Chafing gear can be added to the pendant and/or bobstay and inspected and replaced as needed, but that is the best idea I have heard of.

[LazyGuy]

Different answer....same problem. There used to be a Luders 33 one mooring up river from where I am now (well before I moved there) and from a friend that knew the other owner, he had set up that was similar to mine with a bow roller. To avoid chafe, he ran two pennants effectively creating a bridle as Q describes but it used to sail on the mooring driving the boat up onto one mooring pennant then the other. So he dropped one pennant and the boat stopped sailing. That is a large piece of the reason that I have a single pennant and when we have a storm predicted I remove the anchor and run a second pennant that is slack to take over in the event that the first gives way. There will always be swing but within reason, my mooring pennant does not chafe on the anchor with the single pennant.

[Bluenose]

As I look over some of the short stubby type of anchor platforms shown in this thread (and on the web) they seem to me to originate from a set of requirements in the following order. 1) Need, the number and types of anchors, 2) Logistics, what you can actually fit on the bow 3) Aesthetics and 4) Strength and Structural Efficiency.

I say this because even Tim's second design puts a flat steel plate in bending, transverse shear and if the load is off center, torsion. And although you can always make a flat plate thick enough, it isn't the structural shape the would be the most efficient for these types of loads.

I do realize the difficulty in finding a way to get some meat into these tight spaces. My mind sort of goes to a pair of parallel I-Sections that could be infilled with varnished teak. With these channels firmly bolted to the deck and each bow roller firmly bolted to the outboard end of the channel the bending and shear strength would be very well cared for. And if the center infill was well bonded to the channels the platforms torsion efficiency and strength would be improved.

Off course, little of this minutia is important 98% of the time. It is just during extreme, failure loads that I would want the extra beef of an efficient structure.

Cheers, Bill

[Rachel]

Bill,

That sounds interesting. Is there any way you could post a sketch of what you mean though? I can't quite visualize it.

Thank you,
Rachel

[Bluenose]

Bill,

That sounds interesting. Is there any way you could post a sketch of what you mean though? I can't quite visualize it.

Thank you,
Rachel

Hey Rachel,

Okay here is a quick sketch of an idea. I would still want to look a bit deeper before I ran with it.



But what I though I might do if it was me was to trap a piece of teak between two Bronze c-channels (okay, I change my mind a bit from before). I think the Bronze might be a nice touch and bolted and bonded to the teak the bending, shear and torsion should be good. I also like being able to run the deck bolts and the anchor roller bolts through both the teak and Bronze.

For this sketch I just picked a Bronze channel off the web which was 1 inch high. I think I might go thicker and be done with it. I would also be tempted to bolt and bond everything together.

Anyway, just an idea.

And I agree with you... Pretty hard to beat a round stayed bowsprit.

Bill

[Rachel]

Thanks, Bill -- now I see what you mean. I appreciate the drawing.

Rachel

[Quetzalsailor]

It will be great looking.

If you're serious about strength, have a look at how much the bronze adds. Find an engineer or an architect who remembers his/her structures class; buy beer for the engineer or fine wine for the architect, and get him/her to run the numbers. My gut reaction is that the bronze in such a shallow member loaded in bending will not add much to the teak. Every bit deeper (thicker) the channel gets will improve things alot, that is, a 1" board with 1" wide (deep) channel would not nearly be as good as a 1" board and a 1 1/4" wide (deep) channel.

You may find bronze channel in a shape that lends itself to making the anchor rollers. That would be pretty alongside your channels. I suggest using flat head bronze machine screws; ordinary bolt heads will sooner or later take a divot out of you. Bending and sheer stress on the assembly will be highest where the board begins to cantilever off the boat: deeper structure and fewer bolts removing material is better but more bolts for sheer is better; easy enough to calculate. Torsion translates to sheer stress between the wood and the channels, too, but is distributed evenly along the length of the cantilevered part. Torsion is best resisted by something tubular; a flat board and bronze edges is less efficient but there really is not nearly so much torsion as there is bending in this assembly. Cutting that hole for the forestay fitting takes wood, and strength out where the stress is highest; perhaps you can sandwich the board between fitting and foredeck.

[Bluenose]

Great points. I have always found it interesting how little analysis goes into determine the sizing for critical boating components. The Pardey's mentioned this as well and I believe their conclusion was that there is such a limited market for boat hardware and every boat is different so the loads never get calculated and the structure isn't sized or tested until the owner does it under extreme conditions.

As I mentioned my sketch was a conceptual idea. The actual sizing would be dependent the type and size of the boat and the foredeck configuration. But with respect to strength here is the approximate ultimate tensile strength of various metals and woods.

Teak: 15,000 psi
6061 Aluminum: 45,000 psi
Silicon Bronze: 85,000 psi
304 Stainless Steel: 73,000 psi

Even though I believe that teak is one of the stronger woods it really isn't that strong with respect to most structural metals, as Tim found out. I sort of looked at it as a way to support the structural channels and as a place to stand.

I still might rather use a pair of I-beam sections instead of the two c-channels. The c-channels would want to rotate when a download is applied which would need to be reacted by the teak. A nice pair of i-beam would be nice and stout. Although one would have to fill the extra open ends.

I also wouldn't be surprise if you could make an acceptably strong platform using a pair of 6061 Aluminum channels. These are readily available, not too expensive and very light weight.

Any, in the Thanksgiving tradition, excessive food for thought.

Cheers, Bill

[Zach]

Idea:

Big honking eye bolt through the stem close to the waterline. Run a nylon pendant from it to the anchor chain, leaving slack in the chain over the anchor platform.

Now the load won't be anywhere near the platform, and the effective scope of the anchor rode is increased by a few feet, on account of being closer to the water.

Zach

Edit: Also, if you want a beefy bronze channel made... bronze is weldable. The guys that know how to work with it best are the medal sculpture folks that make statues... Though call around to some prop shops to see if they want the job.