Mast for KHSD 30' cat

Hunky

Member
50
5
NW Alaska
Way back in the 1900's when I started this 30' (9m) cat build, and before I knew really much about anything, I purchased a used mast (came off a monohull) that was "about" the right length for the Kurt specified mast. Since, he has updated his drawings and the mast now is over a foot shorter. It has other shortcomings as well - only one set of spreaders, the width moment specified is 6 in4. and mine is 5 in4. The long dimension moment is ok. The mast head has smaller sheaves than spec'd. The head is also welded on, and if cut off the mast would be even shorter. Specified at 37' 7" (11.5m), mine is about 36' 4" (11m). I added a cuddy cabin and the boom would need to be raised now maybe another foot or .3m, making the mainsail even smaller.  It has only one set of spreaders, and is not set up for a fractional rig as the design wants.
 
The other day I called a rigger about perhaps setting up my mast for synthetic shrouds and he talked an hour about why I should not have a shorter mast from design, as well as other considerations. I am to the point of spending some money on this mast to get it set up to work, and then would need know these things to get a good mainsail design. But he got me thinking that perhaps I should seek a proper mast for the design. He admitted it is dependent on use, and unstable weather in NW Alaska could allow for a smaller rig, but these things I just don't know about (except for the unstable weather).
 
Budget is a big factor. At this point I could probably have a motor boat, but to set up for sailing may take a next year launch, so I have a little time. Just a month or two left in this year's season. I have a couple choices. Use what I have and get a mainsail that would work with it, or purchase a new (used?) mast. That way I may even get one that is a bit more toward a wing mast. Mine is an Isomat NG37 off a Beneteau mono. I've yet to acquire a step for it or build one (rotating is the design). I suppose a third option is to build a mast. Wonder if anyone else does that? I asked Kurt about it - he has plans for a plywood/carbon mast that might not be too expensive to build - but he would have to modify his drawings for my size boat. I did build the boom using that technique. Being up in Nome, Alaska, I don't really have the option to have a rigger come up and help out, and it would be difficult to shop for a used mast since I am off the road system.
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Zonker

Super Anarchist
9,128
5,041
Canada
I think the shorter mast is no big deal. But 2 sets of spreaders mean Kurt is assuming shorter panel distances than your mast with 1 set of spreaders. This is a big deal. You can always build up the step 12" higher but you can't fix the basic strength in the extrusion. Adding a 2nd set of spreaders isn't very straightforward. 

Sorry 

 

eastern motors

Anarchist
685
142
Putting that mast on a rotating step would be kind of pointless.  The shape is different on rotating masts.

The real problem with putting a random monohull mast on a multi is the possible difference in righting moment.  

 
What Eastonmotors  said, catamarans are very stiff compared to monos that heel, unless the righting moment of your boat and the mast donor boats are similar your flogging a dead mast. 
A foot shorter on a cruising boat is of no consequence if your going to race then go for more length. 

 

kruiter

Member
57
36
Honlulu
If it were me my goal would be to get it the water and sailing asap.  You can sort/upgrade etc in years to come if you feel the need.  That would mean:  adding a second set of spreaders (I would think), buying sails off ebay, and rigging with dyneema.  I can see that adding spreaders might be more complicated than just bolting them in place, but I cannot imagine that it would be harder, take longer, or cost more than finding your perfect mast and transporting it to your remote location.  All this assuming you are just going to putter around locally for a while and not looking for any major ocean crossings are anything right away.  You might take a look at how dragonfly manage their spreaders etc, as they seem to use pretty wispy mast sections and them add spreaders and such to make them stronger.

 

ziper1221

Member
109
39
florida
I think the shorter mast is no big deal. But 2 sets of spreaders mean Kurt is assuming shorter panel distances than your mast with 1 set of spreaders. This is a big deal. You can always build up the step 12" higher but you can't fix the basic strength in the extrusion. Adding a 2nd set of spreaders isn't very straightforward. 

Sorry 
what is the relationship between panel distances and spreaders?? 

 

Hunky

Member
50
5
NW Alaska
If it were me my goal would be to get it the water and sailing asap.  You can sort/upgrade etc in years to come if you feel the need.  That would mean:  adding a second set of spreaders (I would think), buying sails off ebay, and rigging with dyneema.  I can see that adding spreaders might be more complicated than just bolting them in place, but I cannot imagine that it would be harder, take longer, or cost more than finding your perfect mast and transporting it to your remote location.  All this assuming you are just going to putter around locally for a while and not looking for any major ocean crossings are anything right away.  You might take a look at how dragonfly manage their spreaders etc, as they seem to use pretty wispy mast sections and them add spreaders and such to make them stronger.
thanks kruiter, you sort of nailed it I think as far as what I might be up to for the first bit with this new boat. I'll research adding second set of spreaders, but the existing ones are welded on and probably screw up proportions for adding a second set. I don't know. I'll have to take a look to see if there is any compression tube between existing spreaders. And they are not swept back by very much. I did get a response from Kurt Hughes and he basically said to use what I have and get sailing. Suggested maybe a non-overlap headsail with maybe a genoa on a luff wire (which I think means adding a mini bowsprit).

 

kruiter

Member
57
36
Honlulu
My Horstmann (which is likely not a great example) does not use any spreaders at all.  The top shrouds go to the outer hulls and the mid (a bit below the middle, acutally) shrouds go to the inner hulls.  On mono hulls the spreaders are required to give you enough angle to support the top, but on a multi hull you can sometimes get that just by going to the outer hull.  The drawings from Horstmann shows spreaders and all the shrouds going to the inner hull, but that is not how it was built.

 
Way back in the 1900's when I started this 30' (9m) cat build, and before I knew really much about anything, I purchased a used mast (came off a monohull) that was "about" the right length for the Kurt specified mast. Since, he has updated his drawings and the mast now is over a foot shorter. It has other shortcomings as well - only one set of spreaders, the width moment specified is 6 in4. and mine is 5 in4. The long dimension moment is ok. The mast head has smaller sheaves than spec'd. The head is also welded on, and if cut off the mast would be even shorter. Specified at 37' 7" (11.5m), mine is about 36' 4" (11m). I added a cuddy cabin and the boom would need to be raised now maybe another foot or .3m, making the mainsail even smaller.  It has only one set of spreaders, and is not set up for a fractional rig as the design wants.
 
The other day I called a rigger about perhaps setting up my mast for synthetic shrouds and he talked an hour about why I should not have a shorter mast from design, as well as other considerations. I am to the point of spending some money on this mast to get it set up to work, and then would need know these things to get a good mainsail design. But he got me thinking that perhaps I should seek a proper mast for the design. He admitted it is dependent on use, and unstable weather in NW Alaska could allow for a smaller rig, but these things I just don't know about (except for the unstable weather).
 
Budget is a big factor. At this point I could probably have a motor boat, but to set up for sailing may take a next year launch, so I have a little time. Just a month or two left in this year's season. I have a couple choices. Use what I have and get a mainsail that would work with it, or purchase a new (used?) mast. That way I may even get one that is a bit more toward a wing mast. Mine is an Isomat NG37 off a Beneteau mono. I've yet to acquire a step for it or build one (rotating is the design). I suppose a third option is to build a mast. Wonder if anyone else does that? I asked Kurt about it - he has plans for a plywood/carbon mast that might not be too expensive to build - but he would have to modify his drawings for my size boat. I did build the boom using that technique. Being up in Nome, Alaska, I don't really have the option to have a rigger come up and help out, and it would be difficult to shop for a used mast since I am off the road system.
View attachment 452453

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I have a COMPLETE spare rig for my F85SR Mail Order Bride. Rig includes 37’  rotating  mast, boom, lots of sails all used only three seasons. Contact me if you are interested. Rig is on Vancouver Island.

 

Zonker

Super Anarchist
9,128
5,041
Canada
Masts fail by buckling. Buckling strength is very dependent on unsupported lengths. I.e. Deck to Spreader, spreaders to masthead. If you have a 30 ft mast with 1 Spreader the panel length is about 15 ft

 With 2 spreaders it is more like 10 ft panel length. So the moment of inertia for a 2 Spreader mast can be much lower. The formula for buckling is actually proportional to L squared. Thus 10 ft panel is about 2.25x stronger than 15 ft panel

 
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