Marblehead rigging

Ok, one last question. (or not) I’m using a deck stepped groovy aluminum mast that’s about 7.5’ tall. I’ve got Rod Carr sails that is jackwired to the mast using these little double tubes. I can’t seem to find in my notes or plans anywhere how I was planning on rigging up the shroud wires. It seems that the latest thing to do is go shroudless, but it is too late to build a shroudless system onto my boat.

If you still have shroud wires on your M-Boat, How did you do it? Did you use double shrouds, diamond shrouds and/or spreaders and where did you locate the attachment points and spreaders?


In order to have a shroudless rig, you would need it to be keel stepped with good deck partners. You would also want a very stiff mast (I doubt that your aluminum rig is anywhere near stiff enough for that). So, unless you aer willing to buy a carbon mast and re-do your deck/keel structure to build a keel step and deck partners, I think it is too late.

The amount of rigging you will need depends a lot on how rigid your mast is and how much rig tension you are running. I would start with a simple singel spreader rig with single stays. Do not go with the short spreader designs that many have been playing with. This has been discredited as being a really bad idea. Go with long spreaders about 40%-50% up the mast with the shrouds attaching to the mast about 80%-100% of the way up. You will want to try and evaluate how much mast bend you have with that rig. You may find that the mast has too much lateral bend, then you can add some lowers. If that is still not enough, then you can add some upper diamonds or whatever is needed to correct the area where the bend is occuring.

Pay attention to your fore/aft bend as well. If you are getting a lot of bend fore/aft because of backstay tensions needed to control the jib luff and leech, then you might want to consider moving your lower sidestays a bit aft on the chainplate. This will allow you to use them as checkstays to hold the center of the mast aft and countol your bend.

Make sure you use low stretch rigging line or wire for the rigging. I also believe in using turnbuckles as it is much easier to make fine tuning adjustments at high tensions with a turnbuckle rather than bowsies.

Hope this helps…

  • Will

Will Gorgen

If you are using an aluminum groovy mast on an M boat, then you will need all the rigging you can deal with. These aluminum groovies are already to bendy IMHO for IOMs let alone M boats.

Uppers attach about six inches or so down from the very top of the mast. These run trough the spreaders witch are about what Will says, 40 to 50% up the mast. I would then have them attach to the deck about an inch back from the mast step.
Lowers should attach as close to the spreaders as possible, just under. These should then attach to the deck at about 1 1/2? back of the mast step. I would then consider a diamond stay from the top of the mast through the same spreaders down to the base of the mast. These need to be adjustable and can be do so with either a turnbuckle at the base or a small tube, or even a swag, that can slide up and down with both sides of the diamond stays running through it.

Now, another big problem with this mast is that the boom lift will bend it right at the lower section, so check stays, or lower-lowers, should be used, but this will give little room for the boom to swing all the way out . Consider a mast strut at the front of the mast.

I would just consider buying a good CF mast myself.

Thanks guys. Just what I need to get started. Just to clarify, I’m using the .75" airfoil shaped mast, not the little .5" round groovy mast.

The Cf mast is on my shopping list!! [:)]

I am not sure how stiff the 0.75" airfoil shaped mast is; it may be stiff enough to get away without the diamonds or even the lowers. Start with just the uppers. Sight down the mast WHEN IT IS LOADED at the top of the wind range for your rig and look at the lateral bend. Lateral bend is bad as it will totally destroy your carefully tuned twist. If you see any lateral bending at all, then you need more rigging. Try to evaluate where the bending is taking place and evaluate what additional rigging is needed (lowers to cue mid bend, diamonds to cure upper bend, etc).

Greg is right about the boom causing bend low in the mast. Although the airfoil mast is stiffer fore aft than lateral, you may still find quite a bit of bend at the bottom. It is an easy thing to check for. With your vang set to a normal level of tightness, lift up on the end of the boom and see how much stiffness there is. You may even want to sight down the mast whil someone else lifts up on the boom. You will see the bending. Then you can assess whether the sail shape is changing dramatically in the puffs due to the boom lifting. If it is, then you probably need more stiffness.

To cure this, instead of “lower lower” checkstays, or a mast ram, you may want to also consider inserting a carbon fiber stiffening tube inside the mast. This might be somewhat difficult with an airfoil section, but if you can find a carbon tube that just fits inside the mast, about 12 to 18 inches long and then glued in place, this will add a lot of stiffness to the base of the mast which can cure some of that boom induced bending. Even with carbon fiber rigs I have seen people use doublers near the mast base to add a bit more stiffness…

Take a look at what lester has to say about lateral bend. In particular takea look at what happens to the sail shape for a relatively small amount of lateral bend as shown near the bottom of this page:

Good Luck!

  • Will

Will Gorgen

Lester Gilbert has made some very nice articles discussing verious topics …

Maybe you should take a look at and



The wind tunnel testing that Lester has performed recently has discredited the short spreader theory given in his “spreader” page. I don’t think he would recommend this short spreader design idea any longer.

Lester - If you are reading along - you might want to update your sprerader page to discuss the results of the wind tunnel testing.

  • Will

Will Gorgen

That’s very interesting reading, Will. I think that I do have a carbon fiber tube laying around that might fit inside the mast. [:)]

Here is the article I was looking for. There is more detail on the effect of lateral mast bend on the sail shape. In the conclusion section he discusses how these results show that the short spreader idea was not so brilliant…


I would recommend that you snap some overhead pictures of your rig. you can measure sail shape and mast. You should be able to spot any rig deficiencies. Download this accumeasure software: and it will allow you to put splines on any curve in the picture (it’s designed to measure sail draft but there is no reason you cannot meaure mast bend with it as well…

  • Will

Will Gorgen

Last night, I just finished rigging my Marblehead and all I need to do now is is apply numbers,tape down the hatch and program the radio. It took a bit of work but I got the mast to bend to the shape of the Rod Carr sails. And I think that the boat is just about ready for her maiden. Sure is pretty! [:D]

  1. What do you do with the antenna?

  2. I don’t think I have any waterproof switches laying around. What do you guys do to switch your radio on and off?

  3. Last question is a little more difficult, but how do you set your sails for “weather helm”?



  1. I usually tape the antenna to the underside of the deck. This seems to provide more than adequate reception. The key is to keep it well clear of things that it can snag like sheets, servo arms, etc.

  2. One idea that I have seen that many people swear by is a mangetic switch. I think it is described in the US1M construction manual. The basic idea is that when you put a magnet on the deck of the boat at a specific location (usually the hatch) it will open the switch and thereby turn off the power to the boat. So whenever the boat is ashore, you simply place the magnet on the deck and you will not drain your batteries. Just remeber to rewmove it before you launch.

  3. Tuning for weather helm involves the interaction of several factors. Take a look at Bob Sterne’s tuning guide for some ideas: . The main factor that will have a large effect on helm is mast rake. You will want to rake the mast back to add weather helm (reduce lee helm) and rake the mast forward to reduce weather helm. I set this first (as Bob recommends in step 2 after you have selected your proper rig for the conditions). I use a loop in the end of my forestay that wraps around a “cleat” on the mast such that I get the same rake each and every time I set up my boat. To adjust my rake, I either add or remove wraps of the loop around the cleat. I have a pretty good idea of what rake works best for given conditions, so I can set this up right away and then proceed with the rest of the tuning. After you make the other adjustments (twist, relative trim, camber, etc) you may find that you need to tweak the rake one final time to correct any helm that has developed due to changes in the other parameters.

The only way to assess your tuning settings is to sail the boat. So after you make an adjustment, put the boat in the water and sail around to see if you made the right change. Keep makeing changes (one parameter at a time) until you get the performance you want in terms of pointing ability, speed, acceleration and of course balance.

  • Will

Will Gorgen

Lester has found in the wind tunnel that with one particular setup, long spreaders did a better job than short spreaders. Based on this we have been told by Will that short spreaders are a bad idea, period.

I am curious about the prevalence and apparent wonderfulness of long and short spreaders at the recent IOM National Championship.


Thanks for the link, Will. Bleah, that’s heavy reading but it has already helped a bit.

Magnetic switches, yeah!! I do happen to have a bunch of those laying around. [:D]


Do you have some statistics on who was using long spreaders and who was using short spreaders at the USCGA? Since Lester was there, maybe he noticed this as well. Also did you happen to notice whther the “short” spreaders were actually pulling inward on the sidestays as is shown in Lester’s diagram: ?

There is also the notable difference that most IOMs have mast partners to restrain the lower mast lateral bend whereas the rig that Lester used in the wind tunnel was deck stepped. Rcher specifically stated that his mast was deck stepped as well.

To be clear, what I am saying is that spreaders that are short enough to pull the sidestays in rather than push them out appear to be a bad idea. The theory behind that spreader length was that when the windward sidestay was loaded, it would pull the middle of the mast to windward and thereby open the slot. The real effects of spreaders that are that short appears to be:

  1. to cause the top of the mast to fall off causing the mainsail to twist and to cause overbend wrinkles in the main.

  2. to untwist the jib thereby closing the slot

So, what I am really advocating (and I think Lester probably agrees with me) is that you want to keep the mast as straight (laterally) as possible. In so much as the page Wim pointed Rcher to in his post above was advocating this idea, I anted to point out that more recent testing of that idea showed it to be not such a good idea. So what I am really interested in is what the lateral mast bend looked like for many of the boats at the nationals. Were they inducing a lot of lateral bend? I would be surprised if they were and still able to be competitive. But Lester’s test data may not be the last word on the subject. If more data exists, I’d enjoy digging deeper…

  • Will

Will Gorgen

Just for the record, I made my spreaders about 85% of my beam. My spreaders are removeable so can’t you guys swap spreaders and see what works better for you?

<blockquote id=“quote”><font size=“1” face=“Verdana, Arial, Helvetica” id=“quote”>quote:<hr height=“1” noshade id=“quote”>Originally posted by wgorgen

Do you have some statistics on who was using long spreaders and who was using short spreaders at the USCGA? Since Lester was there, maybe he noticed this as well.<hr height=“1” noshade id=“quote”></blockquote id=“quote”></font id=“quote”>
I didn’t do a detailed analysis of who was using what, but my impression is that most spreaders were between 75% and 50% of beam. That is, no one seemed to be using “short” (under 50%) spreaders.

<blockquote id=“quote”><font size=“1” face=“Verdana, Arial, Helvetica” id=“quote”>quote:<hr height=“1” noshade id=“quote”>To be clear, what I am saying is that spreaders that are short enough to pull the sidestays in rather than push them out appear to be a bad idea.<hr height=“1” noshade id=“quote”></blockquote id=“quote”></font id=“quote”>
As a generalisation, yup, I think you are right, and for the moment I’m talking up spreaders that are somewhere between 75% and 66% of beam… But there is some very interesting detail within this broad picture that one of my wind tunnel students found earlier this year. Just as soon as I can get his report wrote-up from him, I’ll add a Web page (smile). But in essence, he found that “short” spreaders had an advantage in low- to middle-of-rig wind speeds when they apparently worked as theorised – opened the slot just enough to maintain lift and, significantly, keep drag low. When the wind got to top-of-rig, however, it all went to hell 'cos the mast just bent excessively.

Lester Gilbert

I believe Steve Landeau was using less then 50%…