Deck- vs Keel-Stepped Mast

[AussieGeoff]

Originally Posted by roverhi

There is a box like piece of furniture at the forward end of the table. I'll bet that is your mast post or is hiding the mast support post. Your mast probably sits on top of that bulkhead/box.

Ok, I see what you mean. I think you may be right. I'll have to look into that. (Literally lol)

Originally Posted by roverhi

There are a few boats that use a truss system to support the mast. That allows them to get by without a center post. The load still has to be transfered to the keel but it's done by posts/bulkheads off the centerline. The Santa Cruz 27 and the old Columbia 22 come to mind.

Makes sense. Obviously there is more than one way.

Originally Posted by roverhi

Your boat is very nicely finished out. If more cement boats had been built like yours, they be more respected.

Thanks. We only just got her, I haven't even set foot on the boat yet. At $14k for a 35' Ketch, we couldn't let it go, even though it's on the east coast. The fitout is very nice and seems to be original. She was built in 74, apparently in Port Lincoln, not too far from here. (South Australia) She's in Sydney right now, waiting for us to fetch her back to her home waters. The outside is a bit sad though. The paint is mostly gone off the decks and there are some minor rust spots on it as well, plus some damage to a gunwale and a wooden fairing strip, but the hull seems sound and even the broker suggested the interior alone would sell her. She's been a liveaboard at a marina then a mooring since 97.

Oddly enough, we almost knocked her back as the layout is beautiful, but perhaps not ideal for us. There is no permanent double berth, the head and shower are in the forpeak where most boats have a V berth, the saloon table makes up into a double instead. But after looking at the interior and the condition it's in, and the amount of space, we couldn't resist. She needs a darn good spruce up and some minor repairs topside, but seems sound enough.

Most problems in soundly built ferro's are relatively easy to fix, with fairly cheap materials, once you push past the myth and misinformation. I have some money and a lot of time, rather than vice versa, so something I can do myself is my preference.

Cheers

AussieGeoff

[barnakiel]

Originally Posted by Sailcat

(...) I liked what I saw except for the deck stepped mast.(...)

I have sailed a RTW in a boat with a deck-stepped mast. No issues.

If the boat / rig are designed and built adequate to the job in hand, both systems are good. If not, any system can be disaster.

Alas, there are some practical implications:
- keel-stepped masts tend to leak in the deck area and also thru the mast and into the bilges,
- deck stepped masts tend to develop issues around the step area - in some designs, the deck will compress there.

Other than such design-specific challenges, both systems are good as gold for any type of sailing in any kind of weather.

b.

[boatman61]

Owned both and prefer Deck stepped masts for a variety of reasons....
Yes have crossed and would again quite happily...

[Auspicious]

In my professional opinion there is no significant structural difference between a well designed keel stepped mast and a deck stepped mast. Roverhi hit the nail on the head - the biggest difference is increased water intrusion with keel stepped masts.

The items to look for in an aging boat may be different but the implications are similar.

Thus spake a naval architect. *grin*

[sailorboy1]

had both, like my deck stepped better just because it doesn't leak as much, which is a good reason, and this also means wires are not coming out the bottom of the mast in the bildge

I would bet that the support on my current boat is stronger than the mast it supports

[donradcliffe]

From wikipedia on column buckling:

The restraint offered by the end connections of a column also affects the critical load. If the connections are perfectly rigid, the critical load will be four times that for a similar column where there is no resistance to rotation (hinged at the ends).

A deck stepped mast has no resistance to rotation, while a keel stepped mast is like a deck stepped mast with the "end" at the deck held rigid. From the wiki article, it would seem that the keel stepped mast would be about twice as strong as a deck stepped mast of similar cross section, length, and rigging, but I'm too lazy to do the calculations.

[barnakiel]

Originally Posted by Jim Cate

Yes, and a deck stepped mast can jump out of its step and knock a big hole in the deck or house and then go overboard. "I've certainly heard of things like that happening".

Come on, guys... one can imagine failure modes for any setup. There are countless sailboats with both mast designs that have sailed safely for their entire service lives. The design, execution and maintenance of the whole rig is more of a factor in choosing a used boat than which stepping system is used.

Cheers,

Jim

I agree strongly with Jim on this. At least in one installation (ours;-)) there is a bolt that goes thru the mast foot fitting AND the deck step fitting. No way the mast can 'jump out'.

I believe with keel step there is the same story - have the mast tied down (e.g. a piece of rod from the lower portion of the mast to a keel bolt) - and it will neatly break off at the deck level, given the (lack of) strength of the extrusion and the forces involved. NO jumping out, no holes in the boat, no nothing.

If I were to worry about anything then I would avoid some boats with discontinuous rigging where only one stay continues from the lowest crosstree to a single chainplate - one stay goes bang and the whole rig ends up overboard. Seen it happen. This much said, the same set up if properly designed and executed can be probably as good as any.

b.

[zeehag]

my ericson 35mII has a box like that under mast as a corner to head.... is subtle but is the compression post. mine also has an aluminum dish like thing under the mast as a step.....i9s glassed between the deck and compression post....

[goboatingnow]

Originally Posted by barnakiel

If I were to worry about anything then I would avoid some boats with discontinuous rigging where only one stay continues from the lowest crosstree to a single chainplate - one stay goes bang and the whole rig ends up overboard. Seen it happen. This much said, the same set up if properly designed and executed can be probably as good as any.

b.

well , broke a D2( admitidly an intermediate) on one atlantic run, deck stepped mast, 4 days out of teh carrib. Mast held up , we had to be careful amd rigged a bit of a lash up. but it didnt "ends up overboard".

Most case if a main shrould goes, things break, though not always.

Dave

[Unicorn Dreams]

1,000's of each design cruise the oceans all the time. I don't believe there's an issue as they are designed that way.

My boat has both, keel stepped main and deck stepped mizzen...

[skipmac]

Originally Posted by MarkSF

Keel stepped : Check the mast base very carefully for rot, especially on Catalinas.

And Pearsons. Been there, done that, have the photos.

[barnakiel]

Originally Posted by goboatingnow

well , broke a D2( admitidly an intermediate) on one atlantic run, deck stepped mast, 4 days out of teh carrib. Mast held up , we had to be careful amd rigged a bit of a lash up. but it didnt "ends up overboard".

Most case if a main shrould goes, things break, though not always.

Dave

Yes.

I meant 'one thing goes bang' - meaning the lowest elements - stay, tang or chainplate. This is the solution e.g. on Bavarias (but not only) - multi-spreader rig but ZERO extra safety in rigging. I think in an offshore cruising boat, if there are more than one shroud, it is so nice to have them all continue to the deck and have a separate chainplate each. Sure there is more weight aloft, but if one element goes then you still have a good chance of saving the rig.

b.

[Jim Cate]

Originally Posted by barnakiel

Yes.

I meant 'one thing goes bang' - meaning the lowest elements - stay, tang or chainplate. This is the solution e.g. on Bavarias (but not only) - multi-spreader rig but ZERO extra safety in rigging. I think in an offshore cruising boat, if there are more than one shroud, it is so nice to have them all continue to the deck and have a separate chainplate each. Sure there is more weight aloft, but if one element goes then you still have a good chance of saving the rig.

b.

Have not seen many (any?) rigs where the intermediates go to a separate chainplate from the cap shroud. Can't see where the advantage would be structurally. Better to simply design the chainplate so that failure is unlikely, something not that hard to do.

Cheers,

Jim

[barnakiel]

Originally Posted by Jim Cate

Have not seen many (any?) rigs where the intermediates go to a separate chainplate from the cap shroud.(...)

It only depends on how much of a tech freak you are. I tend to spend long moments (ask my first mate and she will tell you 'too long moments') just walking the docks and looking at how boats are made, set up and laid out.

Here a link to what I quickly got off the web:
Sailboat Family: Preparing to Unstep the Mast - Marking the Standing Rigging

In our marina, there is a couple of boats with the same arrangement. The less extreme, and in my eyes still very much desired, solution is to have continuous shrouds even when they end up on the same chainplate. I think when such a twin chainplate is beefy enough this solution is as good or better than the separate chainplates way.

The discontinuous rigging/single chainplate is most common today. It is also the one I like least. In the racing context, I would take it - less weight, less windage, etc.. Yet on a cruising boat, I would always chose the continuous rigging and beefy plates.

b.

[clockwork orange]

As has been said many times both are fine,i personally prefer deck stepped,especially on boats under 30ft. A couple of things i see often see unfortunatly with deck stepped is that many are not well engineered. Back in the spring i rebuilt the mast step/post area on an old Islander 30 where the mast sat on a very light duty cast aluminum base on the cabin top, the core was plywood and extended under the mast (where it should have been removed and replaced with solid glass when built)The mast wiring went through a hole drilled through the mast step,the core and down the corner of the compression post. Of course water had come down inside the mast and rotted out the core,then the post which was smaller than the mast had pushed up through the core,pushed the glass up and broken the mast step casting and left a bit longer would have gone on through. There were so many things wrong with this settup but it lasted nearly 40 yrs. I looked at a Ranger33 a month ago where the post was on the corner of the head bulkhead down to the molded cabin sole with a longitudinal member between 2 floors between the sole and the keel,everything was in great shape except there was a gap between the sole and the longitudinal. The thing is if well designed and executed they are great but need to be thoroughly inspected if buying.
Steve.