Bowsprit 40cm off the center possible?

[Tupaia]

The original (factory) composite bowsprit has a web on the underside, a moulded martingale to prevent bending failure around the cross beam and it is also quite wide at the point it fixes to the cross to resist bending from the sideways forces. There will also be an element of shear on the fixing between the bowsprit and the cross beam. You are planning to use a simple unstayed 80mm ali tube, is the moment of inertia sufficient to resist the bending and buckling forces. I would have thought that you would need at least a martingale to resist the upward force. The upward and sideways forces are considerable several tonnes.

[CaptainRivet]

Originally Posted by Tupaia

The original (factory) composite bowsprit has a web on the underside, a moulded martingale to prevent bending failure around the cross beam and it is also quite wide at the point it fixes to the cross to resist bending from the sideways forces. There will also be an element of shear on the fixing between the bowsprit and the cross beam. You are planning to use a simple unstayed 80mm ali tube, is the moment of inertia sufficient to resist the bending and buckling forces. I would have thought that you would need at least a martingale to resist the upward force. The upward and sideways forces are considerable several tonnes.

Thanks for all the additional info on the orginal bowsprit i didn’t know but was expecting.
That also shows that still all the forces are transfered to the crossmember and that it can take these forces.
You are right that the orginal is quite wide, so the point loads are smaller then when i go via the anchorroller.
But you are right it might be better to add bobstay bridle or however you call this 2 dyneema ropes going from tip of bowsprit to the hulls on a cat.
I like the solution of trogear without dolphin striker the friction rings going to cleats, have already 2 on the crossmember for the mooring lines and can reuse it for the bowsprit:
https://trogear.com/rigging/

[catsketcher]

Go underneath

I have some similar issues to you Rivet.

I already have an articulating 1 metre long sprit that has guy lines out of Dux. It is okay but it does wobble and it is a bit agricultural.

I was at a storage place and a guy gave me a boom from a 38ft mono. I cut off the bomo ends and it just fitted nicely. I have made a composite mount for it under the bridgedeck and walkway (I have a walkway centreline on my net area). I haven't mounted the thing yet, but it will be able 1 metre out front and have no stays - it is pretty husky and I don't pull much on the screecher halyard.

I make composite parts instead of welded parts for masts and booms and such. So the connection of the sprit and the crossbeam will be fibreglass. I can easily take a part off the sprit and the forebeam and then glass together and then bolt onto the underside of the forebeam.

So we will end up with a centreline pole, under the net, much stronger than my current sprit and no hassle with anchor line bridles. I have designed in some slack in the sprit collar to allow for me to move the sprit back at marinas (not that we ever go to them). The other great thing about this is that I can now put my inner forestay further forward so I can have a better staysail for offshore work - I love my little staysail but the pole will allow me to put a forestay out into the net area and get a bigger one - big win.

So go under the net and keep it on the centreline. That roller assembly looks too weak for the uplift to my eye - it will look better and keep your net clean for walking.

[CaptainRivet]

Originally Posted by catsketcher

Go underneath

I have some similar issues to you Rivet.

I already have an articulating 1 metre long sprit that has guy lines out of Dux. It is okay but it does wobble and it is a bit agricultural.

I was at a storage place and a guy gave me a boom from a 38ft mono. I cut off the bomo ends and it just fitted nicely. I have made a composite mount for it under the bridgedeck and walkway (I have a walkway centreline on my net area). I haven't mounted the thing yet, but it will be able 1 metre out front and have no stays - it is pretty husky and I don't pull much on the screecher halyard.

I make composite parts instead of welded parts for masts and booms and such. So the connection of the sprit and the crossbeam will be fibreglass. I can easily take a part off the sprit and the forebeam and then glass together and then bolt onto the underside of the forebeam.

So we will end up with a centreline pole, under the net, much stronger than my current sprit and no hassle with anchor line bridles. I have designed in some slack in the sprit collar to allow for me to move the sprit back at marinas (not that we ever go to them). The other great thing about this is that I can now put my inner forestay further forward so I can have a better staysail for offshore work - I love my little staysail but the pole will allow me to put a forestay out into the net area and get a bigger one - big win.

So go under the net and keep it on the centreline. That roller assembly looks too weak for the uplift to my eye - it will look better and keep your net clean for walking.

Do you have some pictures of the setup please, especially the connection crossbeam to sprit and how this is retractable.

[catsketcher]

Gday Rivet

I have some of the work done, I made some composite tangs for the staysail and the prodder end but no mount yet. I drew these up at breakfast today. They show one idea to make the mount out of something like UHMWPE or similar. I may still make a glass one using uni tow but this one could be lots easier if I can find a nice thick piece of UMWPE - I reckon about 10cm thick and cut it on a bandsaw, or get a plastics place to cut it out.

I have put a hollowed edge on the top where the mount meets the forebeam. That would enable it to sit nicely. I would be bolting this with machine screws that I didn't draw in.

I reckon the nice thing about going underneath is that the mount only takses side loads. And if you give the mount enough area in touch with the forebeam then there is lots of friction also helping the mount to stay where it is along with fasteners.

I made the prodder cut out about 4mm larger than the prodder section. This should allow you/me to undo a bolt at the bridgedeck end in the dinghy and then pull it in for marinas. (Once you get into the marina would be fine I reckon). If it was UHMWPE you could ream it out if needed.

I might go this way or do the uniglass thing but this may give you some ideas.

cheers

Phil

[catsketcher]

One part that is not stated with longerons is that the forebeam does not take any load pushing back. The end where the prodder/longeron meets the bridgedeck needs to be husky to take the compression loads - but this would be pretty easy to make. A socket with a bolt is what I have started making.

[catsketcher]

The only bolt needed for retraction (in the plan in my head) is the single bolt holding the inner end in the bridgedeck socket. I would probably have the prodder/longeron out almost all the time and only pull it in at marinas - and I don't go to them if at all possible.

The boom section I have is light wall but deep enough not to need stays for my loads. So I look forward to not worrying about anchoring and the prodder. Also I will be able to put some weight on in to attach stuff if needed.

[catsketcher]

I really like making glass moulded parts. It is heaps cheaper than getting a metal worker to make the part and I don't have to travel aroujnd finding someone to do it. I put honey wax on the part, do a very light glass surface layer and then go into the shed and add layers and unis and then fair and paint.

I have recently made a new wishbone end for my cat which ties the wishbone ends and a new small section compression post (looks like a boom), a gooseneck for said boomish post, staysail and screecher tangs and all the mast hardware for my little trailer sailer (that was a while ago).

I may make the prodder undermount the same way. Honey wax on the sections. Layup about 2 layers of glass. Take home and glue together. Add lots more glass and the diagonal piece. More glass and trim edges. Stop glassing when piece feels dangerous if I throw it at something. Then fair and paint. Lots of little hour long jobs which is good as I am still working - can get them done in the afternoon/evening. Then go out to boat and tap holes to mount the mount.

Thinking that this method is good because it uses much shorter machine screws. I will cogitate upon the different approaches.

cheers

Phil

[toolbar]

I didn't get that you are using a long pole going from the bridgedeck and protuding just a small bit in front of the front-beam.

In this case no additional compression post is needed of course, because that tube is the compression post.

I would do it just as Catsketcher describes. Put everything under the net and make it centerline even if it is tempting to someow reuse the existing bow-roller-fitting. You will curse the pole every time you hit your toes on it. :-)

I don't think that the pole needs much to hold it in place. Filleting around the tube to fit the front-beam and then wrap some uni-carbon stripes all the the way around the crossbeam and the filleted tube to keep it in place. If you are using waterstays, they will take most of the load and you just need to make sure that the tube does not fall down (and that the point where the tube hits the bridgedeck is strong enough).

Without waterstays the connection to the front-beam needs to be much stronger and take the port/starboard forces as well.

Paul

[Lee Jerry]

Originally Posted by catsketcher

I reckon the nice thing about going underneath is that the mount only takses side loads. And if you give the mount enough area in touch with the forebeam then there is lots of friction also helping the mount to stay where it is along with fasteners.

This is mostly good stuff, Phil, but FWIW, the highlighted bit is wrong. The friction force is not affected by the contact area.

The frictional force is the product of only the coefficient of friction and the normal force between the surfaces. So unless you are doing something else along with increasing the area - like increasing the number of fasteners (increasing the normal force) or adding more “goo” in there (caulk, glue or whatever) - the friction stays the same.

[catsketcher]

I don't quite get friction. I teach it in school physics but its details elude me sometimes. That being said, whem I go out on my bike, my big wide and low pressure mountain bike tyres (even when I had slicks) had more grip than my thin 28mm 100psi road tyres on my road bike so surface area seems to have something to do with it but the how in its details is tricky for me. Certainly in boats, skin friction is totally dependent on wetted surface (which is why racers get the crew forward to lift the flat stern sections of the hull out of the water and why boats for ligther winds have rounded sections). Goo or caulk or fasteners would be a good idea to increase side load resistance.

[CaptainRivet]

Originally Posted by catsketcher

I really like making glass moulded parts. It is heaps cheaper than getting a metal worker to make the part and I don't have to travel aroujnd finding someone to do it. I put honey wax on the part, do a very light glass surface layer and then go into the shed and add layers and unis and then fair and paint.

I have recently made a new wishbone end for my cat which ties the wishbone ends and a new small section compression post (looks like a boom), a gooseneck for said boomish post, staysail and screecher tangs and all the mast hardware for my little trailer sailer (that was a while ago).

I may make the prodder undermount the same way. Honey wax on the sections. Layup about 2 layers of glass. Take home and glue together. Add lots more glass and the diagonal piece. More glass and trim edges. Stop glassing when piece feels dangerous if I throw it at something. Then fair and paint. Lots of little hour long jobs which is good as I am still working - can get them done in the afternoon/evening. Then go out to boat and tap holes to mount the mount.

Thinking that this method is good because it uses much shorter machine screws. I will cogitate upon the different approaches.

cheers

Phil

Great ideas Phil.
Wow what you just do at breakfast is awesome:-)
Why not make the piece underneath crossmember from foam or wood, shape and then just re-enforce+seal it with fibre maybe even carbonfibre.

I just need a 50cm long bowsprit, underneath or on top the bowsprit pole from bridgedeck must be 3m long in total. What do you thik is the minium size in diameter and wall thickness i get away with?
As i said i will mainly use this pole with my 105sqm parasailor flying it deeper to one side and basically using it as a lightwind screecher 80 till 120 degrees. This means it will get significant side forces
As my anchor is retracted at the bridgegeck the pole underneath could get in his/her way.


Another possibility:
I actually won't need a compression post, neither the seldom/nor the other v-carbon bowsprit i posted have a compression post when installed on a Lavezzi and are retractable.
So i could simply use existing bow roller as pivet point for the pole with 2 dymeema lines down to the bows.

[JustMurph]

In a normal prodder on a cat, you're never putting any part of the system in bending. The prodder is only ever in compression. That compression goes into the forebeam, then from the forebeam into the compression post/s back to the bridge deck. That compression post, only sees compression. The side to side and upwards loads are taken by the water stays in tension. None of these loads put the forebeam in bending (i.e. there is no load being transferred from the forebeam to the hulls.

If you can keep all of the loads axial like this, then you can size everything smaller and ligher. If you want to have it in bending (a longeron), then your sections need to get a lot beefier.

You can build your own conventional setup fairly easily, either in aluminium or composites.
I do like cat sketchers approach. That keeps it really simple and keeps the loads out of the forebeam.

[catsketcher]

Gday Rivet

I can understand that you don't want to do the big pole approach - I do want to do it and get rid of my little prodder. Some reasons why.

I don't like bow waterstays. I find them a hassle when anchoring, especially if there is any tide. Mine are above the waterline and Dynex Dux - so they don't work as well as lower ones from wire. Dux is great for many areas but my lines are undersized and stretch a lot. Murph is right with the section idea - but I scored a boom section for my new pole so that is really deep.

It is a real bugger to put the 1 metre prodder out. I think a large pole would actually be easier because my one falls down and I really don't like using the seagull striker to hold it up or hang onto when I put it on.

I also want a staysail tang so the prodder pole will do this as well.

If you wanted to go the under net pole - you could angle it slightly so that it misses your anchor roller. I would have it angled so that it is on the centreline at its outer end.

If you don't use waterstays the engineering gets heavier. The pole would be in bending but that is okay - an oval light wall section would be nice - a 50cm protusion of an under net pole is not a lot of load. I had a quick look at engineering calculators but I can't find one that will let me work out the section you would need. But you will need to start with the maximum halyard load and then multiply this by a safety factor. A good way to start is with the breaking strain of the halyard and go way over this.

As for a short prodder - I don't get why you want to use the anchor roller. Before I got the long prodder I was going to make a moulded glass base for my short prodder. You could do the same. Just honey wax the forebeam, lay up a few layers of 600gm glass over the front half. This would make a fine base for your prodder pivot end. You don't need the anchor roller.

cheers

Phil

[CaptainRivet]

Originally Posted by catsketcher

Gday Rivet

I can understand that you don't want to do the big pole approach - I do want to do it and get rid of my little prodder. Some reasons why.

I don't like bow waterstays. I find them a hassle when anchoring, especially if there is any tide. Mine are above the waterline and Dynex Dux - so they don't work as well as lower ones from wire. Dux is great for many areas but my lines are undersized and stretch a lot. Murph is right with the section idea - but I scored a boom section for my new pole so that is really deep.

It is a real bugger to put the 1 metre prodder out. I think a large pole would actually be easier because my one falls down and I really don't like using the seagull striker to hold it up or hang onto when I put it on.

I also want a staysail tang so the prodder pole will do this as well.

If you wanted to go the under net pole - you could angle it slightly so that it misses your anchor roller. I would have it angled so that it is on the centreline at its outer end.

If you don't use waterstays the engineering gets heavier. The pole would be in bending but that is okay - an oval light wall section would be nice - a 50cm protusion of an under net pole is not a lot of load. I had a quick look at engineering calculators but I can't find one that will let me work out the section you would need. But you will need to start with the maximum halyard load and then multiply this by a safety factor. A good way to start is with the breaking strain of the halyard and go way over this.
Under means also pole is pointing downwards, move it lower on bridgedeck interferes with anchor and would need to be even put more offcenter then my bow roller

As for a short prodder - I don't get why you want to use the anchor roller. Before I got the long prodder I was going to make a moulded glass base for my short prodder. You could do the same. Just honey wax the forebeam, lay up a few layers of 600gm glass over the front half. This would make a fine base for your prodder pivot end. You don't need the anchor roller.

cheers

Phil

Phil i want to use the anchor roller because its there, fully welded to the cross and tested with my roundsail to survive a load i will never reach with the parasailor.
And simple, take the pole, drill a hole, use the bolt of the roller and mount it instead the roller, run the 2 dyneema sheets down to bows and done with it. Cheap, easy, fast done.
See picture attached, thats actually a Lavezzi like mine.
Why not mount that pole onto the anchor roller and set it up exactly like that. Don't need it fold it up.
Yes yours is the perfect solution where you can nearly fly all, don't need that as i said i will only use it for the parasailor when reaching in light wind.

In the attached picture you see how its done and works. they just drill exactly in the middle of the crossmember 16 holes, weaken the crossmember this way and riveting (and get contact corrossion as you cannot tefgel that properly) a little bracket to the center.
A lot of cats have this incl. Lagoons as official factory bowsprit. Well i use bow roller as there, no extra corrossion and no weakening of the crossmember but yes off-center.