Mast modification question (spreaders)

[HoneyRyder]

I am installing a 38' second-hand Proctor mast (cutter rig) on the pilothouse roof of a 44' steel canoe sterned trawler (hull originally built as a sailboat). The masthead will be 50' above the waterline.

The intention is to get a little extra downwind/offwind performance, and to offer a back-up in case of primary engine problems.

The rig has a double set of spreaders.

My question concerns the geometry of the spreaders.

Does anyone know if i can either 1) extend the spreaders a foot or so either side, or 2) run the wire shrouds at an angle away from the mast (not parallel) without imparting the wrong sort of loads on the mast for which it wasn't designed?

If I bring the shrouds down from the lower set of spreaders, parallel to the mast, then they would end up being attached to my deck at an inconvenient position.

The rig also has some running backstays for more support when running.

As my intention is to use the rig for broad reaching and running, rather then for powering upwind (I have an engine for that), I wonder if I can get away with modifying either the length of the spreaders, and/or the angle of the shrouds to the deck.

Any thoughts?

[Privleoplag]

Take a look at a catamaran rigging. If I understand you correctly, the shrouds on a cat are not parallel with the mast, but are aft.

[StuM]

If I understand you, you are concerned that the spreaders are not as wide as the hull and the shrouds will not be vertical if you run then to chainplates on the hull, but will be wider at base than at the the spreaders. If that is the case, it's not a concern at all. Most shrouds are like that.

[PaulSommers]

Talk to a rigger or yacht designer - you could avoid some expensive problems thereby. Hull shape, keel, method of attachment to the deck or hull (including possible need for reinforcement of the deck and/or hull), and the location of the mast base (step) all need to be taken into account.

[Suijin]

Take this input with a grain of salt, as I'm not a naval architect, but the primary point of shrouds are to A) keep the top of the mast in it's generally fixed upright position and B) stabilize the middle of the mast through the lowers to keep it from bowing.

I believe so long as the lower segments of the cap shrouds are roughly parallel, or wider, you'll be fine.

That's not a short mast, and even off the wind there are going to be healthy forces involved. Have you had a naval architect specify what you need in the way of chainplates and reinforcement where they are bolted to the hull?

Also, your boat is not designed for the sort of heeling forces you're introducing. Does it have enough stability? Yes you'll be off the wind, but there are gusts, squalls, and other unexpected events that WILL happen, and your boat's stability needs to be adequate.

Assuming that the mast is deck stepped, you're going to need to either reinforce it or provide support from underneath. There's going to be a lot of downward pressure on it.

[georgelieber]

I installed a second hand 38' mast on a steel 32' Tahitiana sailboat that someone had converted to a trawler. I also removed the trawler cabin and replaced the lead ballast that was removed in the trawler conversion. Luckily for me the ballast came with the boat. I converted the boat back to full sailboat configuration.


That mast is most likely not too large for your boat when it was a sailboat... but it may be a different situation now if there is more trawler superstructure topsides, and/or sailboat ballast has been removed. A 38' mast and sails can apply a lot of force. You probably need a professional assessment of stability.


As far as the spreaders go there should be no problem using wider ones as long as the shrouds make an appropriate and direct path to the deck. The lower sections of the shrouds should be parallel to the mast. The shrouds cannot zig-zag.


Info on my conversion here: https://svecho.wordpress.com/

[foufou]

Aside from the above relevant comments the fore and aft location of the mast is important. Do you have the original design drawings? And ignoring upwind capabilities might be regrettable if your engine lets you down when the only direction to go is upwind. Lots go ponder. All the best

[meirriba]

I would guess that using wider spreaders is an improvement to the integrity of the rig. Of course with proper angle of shrouds to the deck.
This supposing all else is OK, like proper chainplates, mast size etc.
BUT the best will be to consult a good rigger who can see all facts on site.

[Cheechako]

I don't think is any issue with longer spreaders as long as you don't go too far. They are in compression, and the longer they get, the more the spreader cross section needs to be beefed up to compensate. However angles shrouds should not be an issue.
One question though: Although the hull was for a sailboat, are you sure they put the ballast in the keel? or as much ballast as you may need?

[Bor the Wolf]

Just make sure the spreaders aren't pulling the mast. The whole idea is that the spreaders pushes the mast straight. The leeward spreader does little or nothing because the leeward shroud looses a lot, if not all of its tension. That means the windward shroud and spreader are the only controls that push the mast straight.

Obviously, when the shrouds are pulling the spreaders away from the mast and the leeward shroud looses its tension, the windward shroud and spreader will have trouble controlling the mast.

You can have some angle between mast and shrouds as long as the spreaders keep pushing the mast. But you may have to increase shroud tension to create the same forces on the mast/spreader as with parallel shrouds. If not you have two choices, either get longer spreaders of move the chain plates inward.

BTW Proctor, now Seldén, still sells spare spreaders for almost all of its masts, but second hand spreaders from another brand should work too.

[HoneyRyder]

Originally Posted by StuM

If I understand you, you are concerned that the spreaders are not as wide as the hull and the shrouds will not be vertical if you run then to chainplates on the hull, but will be wider at base than at the the spreaders. If that is the case, it's not a concern at all. Most shrouds are like that.

Yes, your understanding of my concern is correct.

And thanks for your comment, that is good to know. I have drawn a picture connecting the dots between the mast head, and both spreaders (the lower spreader is 18 inches longer than the top one), and if i draw a straight line then it ends up in precisely the location that is suitable for a chain plate on the side of the hull.

[HoneyRyder]

Originally Posted by Suijin

Take this input with a grain of salt, as I'm not a naval architect, but the primary point of shrouds are to A) keep the top of the mast in it's generally fixed upright position and B) stabilize the middle of the mast through the lowers to keep it from bowing.

I believe so long as the lower segments of the cap shrouds are roughly parallel, or wider, you'll be fine.

That's not a short mast, and even off the wind there are going to be healthy forces involved. Have you had a naval architect specify what you need in the way of chainplates and reinforcement where they are bolted to the hull?

Also, your boat is not designed for the sort of heeling forces you're introducing. Does it have enough stability? Yes you'll be off the wind, but there are gusts, squalls, and other unexpected events that WILL happen, and your boat's stability needs to be adequate.

Assuming that the mast is deck stepped, you're going to need to either reinforce it or provide support from underneath. There's going to be a lot of downward pressure on it.

In fact it was originally designed and built as a sailboat and has a long, 2 metre deep, 5 ton keel. Without a mast it rolls a lot while at sea, and I suspect that it will roll less when a counterweight like a mast is added. It also has a small mizzen which is a steadying sail, which works well to get it on a heel to stop the rolling.

Re support, I have added a large 7 foot length piece of box section steel to act as a compression post which fits between the underside of the deck and the bottom of the hull (inside), which has been welded and bolted into place, with the addition of 10mm steel plate sections to spread the load (30mm at deck level, 20mm near the hull). I intend to add a 9 foot post made of steel which will be bolted to the deck (topside) and to the pilothouse roof (with a bracket), and the mast and radar will sit on top of that. It is almost certainly overkill, but I don't want to take any chances.

Than k you very much for your thoughts and suggestions, very helpful.

[HoneyRyder]

Originally Posted by georgelieber

I installed a second hand 38' mast on a steel 32' Tahitiana sailboat that someone had converted to a trawler. I also removed the trawler cabin and replaced the lead ballast that was removed in the trawler conversion. Luckily for me the ballast came with the boat. I converted the boat back to full sailboat configuration.


That mast is most likely not too large for your boat when it was a sailboat... but it may be a different situation now if there is more trawler superstructure topsides, and/or sailboat ballast has been removed. A 38' mast and sails can apply a lot of force. You probably need a professional assessment of stability.


As far as the spreaders go there should be no problem using wider ones as long as the shrouds make an appropriate and direct path to the deck. The lower sections of the shrouds should be parallel to the mast. The shrouds cannot zig-zag.


Info on my conversion here: https://svecho.wordpress.com/

Sounds like an interesting project too. Mine will be a motor sailor, or something like it, when it's done. I have retained the pilothouse, and the mast will sit above it on a steel post, so the masthead will be 50" above the waterline. I chose a low aspect cutter rig to keep heeling forces to a minimum.

The lower spreaders are about 3.5 feet wide (each one), so just over 7 feet wide when combined with the mast. Whereas the beam is more like 14'. The top spreaders are only 2 feet wide, which means that over a 38' length of mast plus 9' of post, the shrouds end up at the right place, i.e. at my chainplate location on the hull, unless I decide to move them inwards close to the hull (not impossible, just inconvenient, hence the question).

Thank you very much for your contribution and thoughts. Very helpful.

[HoneyRyder]

Originally Posted by foufou

Aside from the above relevant comments the fore and aft location of the mast is important. Do you have the original design drawings? And ignoring upwind capabilities might be regrettable if your engine lets you down when the only direction to go is upwind. Lots go ponder. All the best

No original drawings, unfortunately.

Re mast siting, I've done the calculations with regard to center of effort and center of lateral resistance, and it looks to be in a good spot, but if not, it will not be hard to make adjustments. I'm considering making an adjustable mast foot so I can play with it a little anyway. Or, I can factor in the effect on the numbers from a mizzen sail too, so hopefully I will be able to get it balanced with a little trial and error.

Many thanks for your help.

[HoneyRyder]

Originally Posted by Cheechako

I don't think is any issue with longer spreaders as long as you don't go too far. They are in compression, and the longer they get, the more the spreader cross section needs to be beefed up to compensate. However angles shrouds should not be an issue.
One question though: Although the hull was for a sailboat, are you sure they put the ballast in the keel? or as much ballast as you may need?

I have 5 tons of ballast in the keel, which makes it roll a lot. I am making a little bet that the addition of the mast will act as a counterweight and reduce the rolling, when I don't have a steadying sail up (due to lack of wind).

Thanks for your help.