Mast Raising Alterations 26M

[Tomfoolery]

Since I used tinypic and photobucket back-when, those pics aren’t there any more anyway. But I always keep the photos or graphics in a Mac photo file, so over time some of them get reposted.

I guessed at the mast weight and CG location, so the resulting forces are also suspect, but the geometry should be right or close to it. You can scale the resulting forces up or down based on mast weight and CG.

The mast on the is shorter and lighter, and the MRS uses the jib (or genoa in my case) halyard, so the forces on the gin pole are definitely lower. There’s also no side forces on the gin pole, as the mast has baby stays. Not much risk of buckling the tangs at the bottom. Maybe not so true for the gin pole, though. I’ve seen pics of buckled tangs, and I’m pretty sure that was on an gin pole.

[Jimmyt]

That is my impression also. All of the stories I've heard regarding bent gin pole brackets were the new MRS design for the 26M. Only about 5 as I recall, or 6 if I count my own... Mine were bent due to excessive mast swaying - which is no longer a problem. Don't know why MacGregor got away from mast-connected baby stays on the M.

Your numbers are close enough to my (corrected) numbers to make me comfortable with my understanding of the loading. I wouldn't want to balance a 500+ lb load on top of my gin pole, without stays, relying only on the brackets to keep it vertical. And, I'm a bit queasy when it comes to depending on those brackets to hold a 500+ lb load - even with stays to keep it vertical.

Thanks again for the load check. I need to do more of that to stay sharp. I've let other interests fill my free time.

[BOAT]

Mast compression load depends on where you attach to the mast. I did this years ago using a level mast, but of course, it's not level at its lowest position.

Yes, I have the 377 pound version and that is why I do not use baby stays on the gin pole - at that weight the failure point would be transferred from the baby stays to the gin pole. That's subverts the whole point of the original system using the baby stays on the MAST and not the gin pole. The MAST will never fail - it's too strong - so the original system puts all the failure possibility on the baby stays which are many times stronger than the gin pole.

The gin pole is the weakest link in the MRS system, not the baby stays.

One of the nicest X systems I saw was just a simple 4 line tackle block - no winch or gin pole needed - if I can find that video I will post it - you guys might like it.

I think a single whisker pole on one side only would be the best solution because the whisker pole could stay attached to the mast at all times and be used for other things too. If Tom could work out the geometry for a single whisker pole side stay for mast raising we could have jimmy weld up one of those because he is so good at welding. (I wish I could weld )

[Tomfoolery]

The gin pole is the weakest link in the MRS system, not the baby stays.

By my calculation, the critical buckling load of the (mast)* gin pole tube (1.5" OD x .125" wall x 72" long) is around 2450 lb. Put some factor of safety on it, and it's still plenty strong, but those flared stamped sheet metal tangs at the bottom are iffy. So is the tube wall where they bolt on, though I haven't checked that connection. Putting a wooden or plastic slug, or aluminium sleeve for that matter, inside the tube at the last few inches at the bottom would be a big help. Keeping it square to the tabernacle would also, as just the slightest off-square puts all the load on just one tang.

*Correction. There is no strike-out option, unfortunately.

[BOAT]

The gin pole is the weakest link in the MRS system, not the baby stays.

By my calculation, the critical buckling load of the mast (1.5" OD x .125" wall x 72" long) is around 2450 lb. Put some factor of safety on it, and it's still plenty strong, but those flared stamped sheet metal tangs at the bottom are iffy. So is the tube wall where they bolt on, though I haven't checked that connection. Putting a wooden or plastic slug, or aluminium sleeve for that matter, inside the tube at the last few inches at the bottom would be a big help. Keeping it square to the tabernacle would also, as just the slightest off-square puts all the load on just one tang.

The factory version uses the back part of the mast plate to support the bottom of the mast. If the mast falls it will bend the angle plates that are bolted to the cabin roof, not the mast or the bolt or the plate. Mastreb already proved that by trying to lift his mast with only one baby stay - the mast fell over and ruined the angle plate that is bolted to the cabin roof. All other parts stayed intact.

So, with the factory system the tabernacle fails before the mast but that only happens if a stay fails and that is almost impossible. The Baby stays are attached to the mast at the bale - not to the gin pole - so even if the gin pole fails the mast is still supported by stays so it falls towards the aft.

If you move the baby stays to the gin pole and the gin pole fails the mast can fall anywhere off the side of the boat because without the gin pole the baby stays no longer work. That's why the baby stays are attached to the mast bale - not the gin pol.

The gin pole is the weakest part of the system - in particular the yoke at the bottom - it could collapse or bend - but if the stays are on the mast bale where they belong they will prevent the mast from falling to the side.

I think the best alternate setup would be a 4 pulley block system off the spinnaker halyard and a single whisker pole mounted to the side. I mean, that would be strong, easy, and simple. It would be more convenient than the MRS but is it really worth all that fabrication to have one?

[Jimmyt]

To be clear, I'm adding stays to the gin pole, in addition to taking the slack out of the mast baby stays. Mast stays of some sort must be utilized to safely raise and lower the mast. The first step in my improvements was to take the slack out of the mast baby stays and connect them directly to the mast. This greatly reduced mast swing on the way up (or down), which greatly reduces stress on the mast base, tabernacle, cabin roof, etc.

After taking care of the mast sway, my next concern was the brackets at the bottom of the gin pole. They appeared to be WAY under-designed to be used with a free-standing (un-stayed) gin pole. I had already bent mine once. Since a couple of folks, beside me, voiced concerns about the bottom brackets and how they might be reinforced, I decided to look at the loading (getting schooled by Tomfoolery in the process).

Bottom line, I thought that mast swing, or me slipping, losing my balance, etc and grabbing the gin pole to steady myself were two likely hazards that would probably result in bracket collapse and loss of mast control. Adding stays to the gin pole and tightening the mast baby stays addressed those concerns. After getting a fairly firm handle on the loading of the gin pole, I looked at the design of the bottom bracket and was not tickled pink with what I saw. So here we are.

In my opinion, if you get the mast up to about 30-45 degrees, have something hang up, walk back to clear it, slip, grab the gin pole and take it down, the metal brackets at the mast step will not be the only thing that gets damaged. But, if you're happy with the stock arrangement, you can sit back and be entertained by me as I idiotically fix something that ain't broke. Been doing it all my life.

[BOAT]

It's not about fixing what ain't broke - I think improvements are always a good idea.

I spent a lot of time working on the mast plate trying to create mast rotation locks and mast sensors for wind indicators and I have worked those bearings on mast plate connection and everytime I try to improve it I end up removing whatever I did. It drives me crazy. Take the mast plate where it bolts to the mast with that big bolt - the mast rotates on that thing - there are incredible forces on that bearing.

In two years I ruined three sets of those BWY "improved" bearings that replace the washers. After 5 years of screwing around with bad bearings guess what? I'm back to the stock washers! The force on the BWY bearing is too great - it grinds them right out.

That bearing is also why the mast swings wildly in the lower positions (the nut is loose! that's what my wife says about me))- if you pull the mast tight against the boat to stop the waving your actually pushing on the mast plate at a pretty good angle against that main bolt stud. I tried that adjustment too (I made the baby stays tighter) - then I noticed the strain was all being transferred in a cockeyed angle to that mast stud on that plate and I said - "Well, that was a bad idea".

Roger drives me crazy - I always think I have a better design only to end up back where HE started.

It's true that in the lower position the mast is really in a "cradle" position able to sway but rest assured that's what you want because what your doing is lifting the mast sort of from the middle straight up - in that configuration the pressure on the mast plate is NOT downward pressure but UPWARD!

It sounds counterintuitive but you can see it in Toms drawing - his first drawing has the mast plate being pulled upward in the lower state but in the second drawing the mast plate is being COMPRESSED in the lower state.

The geometry is crazy. That's why I sort of wanted a single whisker pole to one side and a long tackle to the higher spinnaker bale but I don't know if the tabernacle can take the compression - I think it can. (Only Tom knows for sure)

I'm not sure what stays on the gin pole really accomplish. I agree that your reset of the geometry of the mast baby stays are a great idea - I'm just not sold on yet another set of stays for the gin pole. I need to think about that one.

[NiceAft]

I can relate to the swaying mast problem when raising the mast. In my case, the problem is water skiers.

When having a slip for two weeks on Huddle Bay in Lake George, NY, the wake from waterski boats causes havoc if u try to raise the mast. I now do it early in the morning, but the occasional water skier ruins even the best plan.

The brackets at the base of the MRS pole have been severely bent out of shape. Fortunately, Kevin lives not far from me, and his metallurgy skills have saved the day. I have though, ordered a spare pair for the next time. Kevin may not be close at hand

Ray



Me getting instruction on how to temper the metal brackets.

[BOAT]

A whisker pole mounted to the side would solve that problem too.

There seems to be a real need for stabilizing this operation.

In my case I think about all the low bridges I need to get under when i go to Los Angeles or San Diego.

[Russ]

Fortunately, Kevin lives not far from me, and his metallurgy skills have saved the day. I have though, ordered a spare pair for the next time. Kevin may not be close at hand

Ray



Me getting instruction on how to temper the metal brackets.

I wish I lived close to Kevin. My bracket needs some of his magic.

[Jimmyt]

I'm not sure what stays on the gin pole really accomplish. I agree that your reset of the geometry of the mast baby stays are a great idea - I'm just not sold on yet another set of stays for the gin pole. I need to think about that one.

Thanks for the mast baby stay comment. I'm pleased with that result.

Not really trying to sell you on the idea. You're a smart guy with a ton of experience with your boat. I just don't think the stock setup is safe to be used without some sort of side bracing (stays, rigid diagonals, etc).

In my opinion, the gin pole baby stays secure the top of the gin pole, so it can't deflect sideways. Without stays, that wimpy bracket has to take any side loads on the gin pole - which is why they get bent like Ray's and mine. Somehow we side loaded it.

Taking it to a rather extreme analogy, you wouldn't try to keep your mast vertical using only a forestay and backstay. The bracket at the base of the mast couldn't resist the loading if the mast got even a fraction of a degree off vertical. The gin pole is just shorter. But, it has a 377 to 500+ lb load sitting 6 feet off the deck pushing down on that skinny pole - just poised to strike - if that bracket lets it move a bit off vertical. But now mine won't. And, I have something to lean on or grab if I lose my balance. I think it will really help when mast raising afloat, which, as Ray points out, can be exciting due to circumstances beyond our control.

I don't suppose you have a sketch of your whisker pole idea? I'd be interested to see what you're thinking. I'm having a little trouble envisioning it.

[Jimmyt]

One more point BOAT... The gin pole stays were Highlander's idea. I just thought it was so good I copied him. But if you think it's a loser, you could share the grief with him too!

Sorry Highlander. Getting lonely here under the bus...

[BOAT]

I will make a picture and post it for Tom to analyse.

[Jimmyt]

I will make a picture and post it for Tom to analyse.

Thanks! Looking forward to that.

[Highlander]

One more point BOAT... The gin pole stays were Highlander's idea. I just thought it was so good I copied him. But if you think it's a loser, you could share the grief with him too!

Sorry Highlander. Getting lonely here under the bus...

Bus what bus ! sounds more like a bulldozer !

J