Converting keel stepped mast to deck stepped

Maybe you should read those documents.

The calculations for the compression load of the mast has nothing to do with fwd and aft lowers, or aft lowers with babystay.

 

Michael, thank you for interesting reading. However, even if lower stays + baby stay can stabilize a rigg that is not to say that a deck stepped mast cannot work without them. I suppose if you look around you will find more than enough boats with deck stepped masts to proof that. I agree with Paul that a properly designed mast step and definitely a tabernacle should take care of the mast not suddenly jumping over board.
Regards
Walter

 

There are millions of boats with deck stepped masts. Everyone Ive sailed had aft swept spreaders or double...fore and aft lowers...not in line rigging. I have never sailed a deckstepped boat with inline rigging and a single lower . Your boat appears to have inline rigging.

When the mast passes thru the deck on a keel stepped rig, the mast partners...deck collar ...stiffens the mast section and keeps it in column. A deck stepped mast has no mast partner and must rely on lower shrouds to keep the mast in column. If the mast gets out of column, athwart ships or fore and aft, it looses rigging tension and jumps off its deck mast step.

Fore and aft lower shrouds...any shroud that pulls down... adds to compression loading. You should not simply covert this rig from keel to deck step.

 

So, since you have never sailed on one they must not exist? Somehow they do.

I've seen hundreds of deck stepped masts rigged with single in-line lowers. I've never seen one jump off the step. Never heard of one. If the rigging somehow came loose enough for the heel to jump off the step I would expect the mast to have already broken.

Based on this logic, if it was true, we should expect a rig with double lowers to have more compression load than a rig with single lowers? That is counter to what you have written earlier in this thread.

 

I find myself in the rare position of defending Paul B. Interesting you've once again jumped to an unfounded conclusion Michael, in which you clearly are letting your "expertise" show again and of course you're in way over your head as usual. Paul is quite correct, as he often is and just because you haven't experienced it Michael, doesn't mean it doesn't exisit, it just means you haven't seen one.

Yep, single lowers in line are quite common and the lowers keep the stick in column, not compression Michael. Again Paul is correct in that if something did give, it would likely be a broken mast, though I'll add steps do often fatigue for various reasons. I've replaced quite a few cast aluminum steps, because the "ears" have cracked or broken off.

Lastly, Paul you'll find Michael gets flustered and contradicts himself frequently in threads. I have to admit to picking on him (repeatedly) for this very trait of his, though none especially recent.

 

I've got a deck-stepped in-line mast. It's stayed up there in a fair bit of breezy coastal racing. You can clearly see the in-line lowers restricting the lower mast bend.

Mind you, when it gets nasty the lower backs are nice and tight, and I'm changing to back to swept spreaders to get rid of the runner hassle soon.

 

I hope everyone reading this thread will inspect their mast step the next time the rig is out. If it is a casting remove it and replace it with a weldment. Cast steps have been popular for many years due to their low price and availability to fit the sections for the big spar suppliers (ISOMAT, KENYON, Schaefer, etc). They are not the best choice of material for the application.

I have read quite a few things he has written that were not correct.

Every harbour has a handful of denizens who seem to think washing boats for a living makes them experts on design, build, and sailing skill.

 

Thanks very much for posting the facts to help Northman with the question at hand. However, we’ve now had the jab and counter-jab so let’s please try and keep the discussion civil. Thanks.

 

Thank you for reminding us!
In the meanwhile I found some information besides the rigging questions discussed here.
The main issue addressed there is that keel stepped masts apparently are thinner walled extrusions (http://www.cruisersforum.com/forums/f47/converting-keel-stepped-to-deck-stepped-mast-50192.html, http://www.sailnet.com/forums/seamanship/1055-deck-stepped-vs-keel-stepped-mast.html, http://www.bayacht.com/aaa/nl-artic/DeckSteppedMasts.pdf).
I wasn't aware of this. Any opinions? Has anybody converted a keel stepped to a deck stepped mast on a sailboat in the 35 to 40 ft range?
Regards
Walter

 

Constraining a keel stepped mast at the partners makes the lower part of the mast (in particular) considerably stiffer. This is accounted for when specifying a keel stepped rather than a deck stepped mast. Whilst a similar effect can be gained by using a substantial tabernacle, you then have to ensure then coach house roof can resist the lateral bending moments created by this as opposed to the simple compression you get with a plain mast step. This stiffness in the lower section is also useful in absorbing the gooseneck loads, especially the lateral loads when running in heavy airs. Again you would have to be convinced that your section could resist these without the benefit of being a fixed ended beam.

If the mast is of a 'chunky cruising section' it may be suitable for conversion. But just have a mast supplier spec you the section for a deck stepped mast with your staying set up and compare it with the section you have. If it's the same or better then go ahead and convert yours to a deck stepped mast. If it's not, don't. Simples.

Locating the mast heel in the mount doesn't depend on staying arrangement. However you might notice an increased need to use the runners to prevent pumping after you convert.

 

I have been following this thread, but have yet to understand the desirability of making the conversion. It would cost a lot of money, you still have the cabin broken up by the compression post, and the end result is traditionally less desirable than what is there now.

Is it possible? Sure with enough money. But if you bought the boat for 100k then spent 50k in the conversion, all to end up with a boat worth less than you paid...

 

Plenty of people with fairly stout keel-stepped masts have had a weather spreader or shroud fail hard on the wind and if quick enough in the tacking have saved the mast.
With a deck-stepped rig, any failure usually puts the mast in the water to leeward at once.
One more reason, added to Stumble's pointing out the use of common logic, to just go sail the boat.
By the way, once a racer with a deck-stepped mast in the heat of the moment misjudged the clearance to BERTIE's bowsprit, caught a shroud on the tip (we were at anchor at the time) and had his entire folded up rig in his cockpit in three pieces in a couple of seconds. Luckily no one was hurt. I looked and looked over Bertie's rig and couldn't see where he had hit me.
Another time WANDERBIRD, an 80' gaff schooner under full sail in the Master Mariners Race in SF, used her fore gaff to foul a ketch by his stout keel stepped mizzen mast and dragged him backwards at 8 knots, filling his cockpit and nearly sinking him because his mast was so strong. The schooner's gaff broke at the same time the ketch's mizzen mast failed and nobody died but it was scary. The ketch tried to sail by 20 feet away on a reciprocal course through our lee to take pictures, was blanketed by our sails making him stop heeling and putting his mast right in the foresail.
Muffinbrain.

 

It definitely is.

Thanks, thats good hands-on advice. I think I will do just that and see what I get.

Walter

 

It's simply a matter of preference. I don't want a hole in the cabin roof when I can avoid it and a compression post will be much less intrusive inside than the huge mast section.

If a conversion would come anywhere near 50k its out of the question anyway

 

The diagonals including the lowers, do indeed, keep the mast in column, but I beg to differ with you, Par, with respect to any side rigging not adding to compression in the mast. If there is a load on the lowers and there will be - how does it resolve itself at the mast without adding to the compression? From the top of the mast down, as the boat heals the diagonals are each adding to compression in the mast (as well as the stays - but from different sources). Google "resolution of force systems" or something similar. There is no way you can load a diagonal without compressing the mast.