Differing shroud tensions affect sail?

[BAD ORCA]

Just curious. when i removed shrouds i noticed forward lowers were equally tensioned but tensioned lower than aft lowers. would this possibly have been intentional and had a specific effect on sail trim/performance?

im at the stage after being back in water of tightening and re-adjusting rigging and am wondering if i should tighten all lowers to equal setting or try to copy what it was set to and play with rig tension a bit while sailing.

 

[dlochner]

Just curious. when i removed shrouds i noticed forward lowers were equally tensioned but tensioned lower than aft lowers. would this possibly have been intentional and had a specific effect on sail trim/performance?

Yes. Forward lowers are typically tighter than the aft lowers. The forward act to induce prebend in the mast, the aft to keep it from going too far and to reduce mast pumping.

im at the stage after being back in water of tightening and re-adjusting rigging and am wondering if i should tighten all lowers to equal setting or try to copy what it was set to and play with rig tension a bit while sailing.

That's a good place to start, however, don't assume the prior owner knew what he was doing. There are a number of good tuning guides out there. Selden Mast has an excellent guide on their website that can be downloaded. Ivar Dedekam also has good book on tuning the rig (Amazon Link).

 

[jssailem]

Based on your boat being a Mariner 36 masthead sloop designed by Philip Canning.

Your sailing rig is similiar to my Cal35C.

Basics regarding stays and shrouds.
The shrouds should be taut enough to maintain the mast in column. The for and back stays should start out the same.

BoatUS has this "expert insight" as to how to start. It is consistent with how I learned to tune my boat.

https://www.boatus.com/expert-advice/expert-advice-archive/2019/april/tuning-a-sailboat-rig

Once the basics are set then you need to take the boat out in about 10 knots and see how it sails. Your going to tack and check the mast for being vertical, the lee and windward shrouds for how they maintain the mast in column. Adjustment to the fore & aft stays address the amount of rake in the mast desired. I installed an adjustable aft stay which allows the mast to be angled aft to maintain the forestay taut (taking any bend out of the furler extrusion) while goign up wind and eased while going downwind.

 

[BAD ORCA]

Yes. Forward lowers are typically tighter than the aft lowers. The forward act to induce prebend in the mast, the aft to keep it from going too far and to reduce mast pumping.



That's a good place to start, however, don't assume the prior owner knew what he was doing. There are a number of good tuning guides out there. Selden Mast has an excellent guide on their website that can be downloaded. Ivar Dedekam also has good book on tuning the rig (Amazon Link).

Mine were the opposite. Rear lowers were tighter. My mast had no noticeable rake in it and was always strait in column. My spreaders have a slight forward sweep to them a couple of degrees. She sailed beautifully on all points of sail but i wouldnt mind playing with the tuning a tad if for no other reason than to learn something.

Thank you. I will look into that guide. Currently I just tensioned everything equally at approx 7% breaking strength. I did caps first to align the mast and then did lowers. I still need to fabricate all my final mast wedges from something and think about what i might use to seal the base, so for now i have it just snug to keep everything steady in the slip.

 

[dlochner]

Is this a wood mast?

Forward swept spreaders seems unusual. Typically, masts should have some rake aft and some prebend. A forward raked mast would cause lee helm, which is not desirable as it can lead to unintended jibes. Rake and Prebend are often not well understood and easily confused. Rake is the degree to which the mast leans aft. It is measured by hanging a plumb bob (the main halyard works) from the masthead and measuring the distance from the aft side of the mast at deck level to the plumb bob. Prebend is the amount of curvature in the mast, it is there to prevent the mast from bending forward and to make it easier to bend it back by increasing tension on the back stay. It is measured by taking the main halyard and running to the base of the mast at deck level, it is the distance between the halyard and the mainsail track at the widest point.

Earlier I said, don't assume the prior owner knew what he was doing. I'm beginning to think he really didn't know what he was doing. I'm speculating here, however, the forestay maybe too short and the spreaders are on backwards. This would cause a negative rake, i.e., the mast leaning forward (a bad thing). The PO may have tried to correct this by over tensioning the aft lowers to pull the mast back and straight.

Cap shrouds hold the mast in column and the mast head centered over the boat. The lowers and intermediates (if you have them) keep the middle of the mast straight from side to side. When there are forward and aft lowers, the forwards are there to help hold the prebend in place in addition to keeping the mast straight side to side. The aft lowers counter the diagonal pull of the opposite forward lowers and to keep the mast straight side to side.

The Dedekam book is a good practical hands on guide to mast tuning, the gospel is the late Brion Toss's The Complete Rigger's Apprentice (Amazon Link). With a wood mast, consulting with a good rigger who knows wooden masts might be worthwhile. Another resource might be a wooden boat forum like Wooden Boat.

think about what i might use to seal the base

I am working with Mystic Seaport Museum Boatyard to build a couple of wooden masts. Sealing the base is an issue because the original masts rotted out from a poorly designed mast step. The Boatyard suggested setting a tenon in the step and a mortise in the mast base and then filling the mortise with grease. When the mast is stepped, the grease squeezes out across the base of the mast, providing an additional seal and reducing abrasion on the epoxy saturated mast butt. The mortise and tenon may not be an option for your boat, grease and epoxy might help.

 

[BAD ORCA]

Is this a wood mast?

Forward swept spreaders seems unusual. Typically, masts should have some rake aft and some prebend. A forward raked mast would cause lee helm, which is not desirable as it can lead to unintended jibes. Rake and Prebend are often not well understood and easily confused. Rake is the degree to which the mast leans aft. It is measured by hanging a plumb bob (the main halyard works) from the masthead and measuring the distance from the aft side of the mast at deck level to the plumb bob. Prebend is the amount of curvature in the mast, it is there to prevent the mast from bending forward and to make it easier to bend it back by increasing tension on the back stay. It is measured by taking the main halyard and running to the base of the mast at deck level, it is the distance between the halyard and the mainsail track at the widest point.

Earlier I said, don't assume the prior owner knew what he was doing. I'm beginning to think he really didn't know what he was doing. I'm speculating here, however, the forestay maybe too short and the spreaders are on backwards. This would cause a negative rake, i.e., the mast leaning forward (a bad thing). The PO may have tried to correct this by over tensioning the aft lowers to pull the mast back and straight.

Cap shrouds hold the mast in column and the mast head centered over the boat. The lowers and intermediates (if you have them) keep the middle of the mast straight from side to side. When there are forward and aft lowers, the forwards are there to help hold the prebend in place in addition to keeping the mast straight side to side. The aft lowers counter the diagonal pull of the opposite forward lowers and to keep the mast straight side to side.

The Dedekam book is a good practical hands on guide to mast tuning, the gospel is the late Brion Toss's The Complete Rigger's Apprentice (Amazon Link). With a wood mast, consulting with a good rigger who knows wooden masts might be worthwhile. Another resource might be a wooden boat forum like Wooden Boat.



I am working with Mystic Seaport Museum Boatyard to build a couple of wooden masts. Sealing the base is an issue because the original masts rotted out from a poorly designed mast step. The Boatyard suggested setting a tenon in the step and a mortise in the mast base and then filling the mortise with grease. When the mast is stepped, the grease squeezes out across the base of the mast, providing an additional seal and reducing abrasion on the epoxy saturated mast butt. The mortise and tenon may not be an option for your boat, grease and epoxy might help.

Nope, my boat has an aluminum mast. Previously it had what looked like teak wedges haphazardly spaced at deck level holding the mast taught, then they filled in around them with lots and lots of silicone to seal up the deck penetration. I destroyed the wedges trying to get all of that silicone out so now have to make new ones. Currently i have soft wood wedges in there temporarily holding everything sort of in place. I'm considering ordering some black locust wood for new wedges or possibly making some polyethylene ones. The polyethylene has a softness and slight compressibility to it and will not rot so should mimic a good hardwood. Just need to reset the mast position slightly to get exact measurements for the wedges. I think i will then fill in around the wedges with casting urethane rubber to seal everything up similar to Spartite.

I think the rigging has not been attended to in a very long time. I have had the boat for seven years and never touched it. My guess is there was some stretching possibly of wires. The % breaking strength tensions were pretty low on everything except forestay and backstay. She sailed beautifully though. She had slight weather helm until i started messing with the outhaul and then she was very balanced after i adjusted it.

The forward rake of spreaders was stock setup on these boats so i'm told and was intentional. Apparently it was intended to help with downwind performance. Its not much, maybe 2 degrees at most, maybe less. The topic had come up in an owners group discussion at one time and explained it in more detail but i forget the details. The mast definitely had no perceivable negative rake considering the condition of everything but i definitely want to do this correctly. She sailed well, but as you mention it doesnt mean it was done correctly.

I downloaded the Selden document which is pretty good explanation. I do have a Loose gauge now as well so can at least adjust to consistent settings. Also, completely forgot i have Brian Toss's rigging book. I need to dig it out and read it.

 

[dLj]

I'd vote for Black locust over the other options you mentioned for wedges.

dj

 

[jssailem]

Brian's book is excellent. You can play with the rake. It will affect the weather helm. 4-5º is standard. If you install an aft stay tensioner, you can actively adjust the mast to improve your trim. Trim the mast, seeking a little weather helm when going to windward. Speed is increased if you can minimize the drag on the rudder while going upwind.