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downeast450 11-24-2009 05:46 AM

Running backstay chainplate placement
 
I am adding running backstays.

When I install the chainplates, what governs their placement athwart ship? I have the bulkheads half done and want to make chainplates. I assume the angle the chainplate is attached should line its running back stay up with the tangs. Since the chainplates are about 5' aft of the mast I will need to either build them with an offset plate for bolting to the bulkhead or build up the mounting surface to accept a flat plate at the appropriate angle. Since I will be building these plates I can design them to exit the deck very close to the toe rail. One thing that occurs to me is stay storage when not in use. How much stress will I create for the wire if they are stored with the lower backs? I have no experience with runningbackstays,yet, and will appreciate any insight.

George

wwilson 11-24-2009 10:20 AM

Runners
 
George,

The runners installed (by manufacturer) on my boat are on the toe rail. The tang is through bolted through the cap rail and the hull/deck joint. The athwart (transverse) placement is therefore maximized, as is the case for every other example that I am familiar with.

You do not mention boat size, but 5-ft aft of the mast sounds very close. In this picture, you can make out the tang for the runners just at the base of the stern pushpit - on the cap rail. On a 40-ft boat, that makes the distance more like 12-15-ft from the mast.

http://www.hallberg-rassy.com/hr39/images/39-27.jpg

The runners are only deployed to support the mast when the inner forestay is used because it attaches well below the mast head. The universal pain in the ass with runners is, of course, that they inhibit the boom when tacking (or gybing). One must be slacked and one tightened for every change of course.

wrt stay storage; I assume you mean a "convertible" inner forestay on which the sail will be hanked when deployed. Mine is stored on the mast. It lays in a notched and radiused fitting at the base of the mast. It doubles back up the mast and then secures via its end-shackle to an eye on the mast and is tightened via its integral turnbuckle. The radiused fitting assures a reasonable bend in the wire. It has shown no damage or deformity on inspection (or very infrequent use) over the years.

Wayne

mitiempo 11-24-2009 12:31 PM

George
Is this on your 28' Islander? How far forward of the mast is the cutter stay and what is your thinking on addind a cutter stay? Are you plannint to sail the boat as a cutter with 2 foresails at the same time? Usually the runner is as far aft of the mast as the cutter stay is forward or close to this. The runner can be made up of higher tech line which avoids the bend doing damage in the case of stainless runners. Only the windward runner needs to be deployed when needed, usually not an issue in light air.
Depending on the reason you have for adding an inner forestay there might be an easier solution. In a lot of cases the inner stay is added to boats with furling jibs so in rough weather a smaller jib than a reefed furler can be set. If this is the case the easier solution is a solent stay. A solent stay is just aft of the forestay and parallels it. Because it is attached so close to the bow and so close to the masthead it doesn't require runners at all. Also because the stay is attached so close to the bow it doesn't require an internal tie rod to the hull in the forecabin. It is a removeable stay. It also makes sense with any removeable stay to use 7x19 wire as it is more flexible and less subject to kinking.
Brian

downeast450 11-24-2009 03:58 PM

Wayne and Brian,
Thank you for your responses. The photograph was a help. Yes, it is for my Islander 28. I am planning to sail it more offshore and want a comfortable and safe sail configuration for higher winds. It is my intention to use it only as a storm sail set up and do not intend to set two head sails at the same time. I am hoping that for my "normal" coastal sailing here I will be able to stow both the inner headstay and the runners out of the way. If I am heading across the mouth of the Bay of Fundy it would be nice to have a storm sail option that was balanced and powerful enough to make progress under adverse conditions. Here is what I am considering. I will mount a chainplate for the inner headstay just aft of the anchor locker. That will give me a thwart under the deck to attach it to. That point is 50 inches aft of the head stay's chainplate. The J measurement of this boat is 11.8 ft. If I want to run an inner headstay parallel to the headstay starting at this point it will attach 24.5 feet up the mast. That would be the location of the tangs. If I use a minimum angle of 12 degrees from the transverse plane of the mast I will be adding the chainplates for the runners about 5 feet aft of the chainplate for the upper shroud. I understand that 12 degrees is a minimum and I do have a good option for a point of attachment that is 6 feet back. I am hoping that the inner head stay can "live" along the rail near the forward lower when the weather does not require a storm set up and that the runners, too can be "stored" conveniently. Using a high strength synthetic line for the runners seems like it will lend itself to that.

What do you think?

George

mitiempo 11-24-2009 04:05 PM

That sounds workable. Remember that the farther aft the runners are the more they will be trying to counteract the inner forestay and the less they will be trying to compress the mast - of course this has to be balanced with ideally being able to beat to windward with one or both runners set while tacking and not having them interfere with the main.
Brian

downeast450 11-24-2009 04:13 PM

That would suggest going with 12 degrees to keep them as far out of the way as possible. Do the chainplates for the runners require a bulkhead for their attachment. I assume they do and I can add whatever I need. I wonder how far down the hull that bulkhead needs to go?

George

mitiempo 11-24-2009 04:47 PM

While they don't require a bulkhead they do require a solid attachment point. A knee glassed in under the deck would work. but I would see if there is already a bulkhead or some other solid point near the desired point of attachment. If so it might make sense to alter the location a bit and use something already available. If not you will have to create one. I would probably make it 10" or so deep and well glassed (with epoxy) to the hull to spread the load as much as possible. Try and align it with the angle of the runner. Use multiple layers of glass (biaxial is best) and make each successive layer bigger in area than the last.
Brian

wwilson 11-24-2009 04:50 PM

George,

I would encourage you to position the tang for your runners as far aft as you can. I have never heard of a "symmetry" applicable to distance forward & aft of the mast in this regard.

The farther back you can position the tangs the more the load on the runners will be in countering the tendency of the mast to "pump" or ultimately bend. As you seem to know - the objective is to stop a buckling of the mast. The force vectors yield more and more to tension (up & down) as the runner attachment points move closer to the mast. You need to counter a force on the mast that will be largely longitudinal - fore & aft.

As far as annoyance, or inconvenience of using runners while tacking or gybing... yes, that is the nature of the beast. Letting the tangs reside forward certainly does open up the arc in which the boom can swing, but it also reduces the protection against a pumping mast - a poor trade.

Wayne

ps as a Maine based sailor I defer to your better knowledge of Fundy. I do have to add that my one sail on it in the summer of '07 was a delight.

tommays 11-24-2009 05:49 PM

On the C&C 35 i sail on there about at the wheel and main sheet traveler which allows the main trimmer to tend them during tacks


Synthetic line has worked very well

downeast450 11-25-2009 04:35 AM

All of this advice has been very helpful. Thank you.

Wayne, You are right, it would be a poor trade to compromise the whole point of having the rig to make having it more convenient.

I have one more concern, supporting the chainplate for the inner. I intend to fasten the inner headstay chainplate through the deck and to the thwart that supports the deck at that point. I have not exposed this thwart yet but expect it to be the same as the rest of the bulkheads. I intend to strengthen the thwart's bond bond to the underside of the deck and the hull with biax and epoxy and add to it if necessary. I am calling it a thwart because it does not continue down to the stem. Do I need to distribute this load that far? I can add knees and thickness to this thwart but a rod to the stem would be inconvenient.

George


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