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-   -   Deck-stepped vs. keel-stepped mast (http://www.sailnet.com/forums/seamanship-navigation/1055-deck-stepped-vs-keel-stepped-mast.html)

psemme 03-31-2001 01:59 PM

Deck-stepped vs. keel-stepped mast
 
In comparing and evaluating the pros and cons of a deck-stepped vs. a keel-stepped mast, it''s become clear that it''s not a black and white issue. Like most everything else on a boat, each one represents a compromise. It would be very helpful for me to hear from any the message boards readers their thoughts on the subject, prefereably acquired through experience. Thanks.

Jeff_H 04-01-2001 10:22 AM

Deck-stepped vs. keel-stepped mast
 
This is a question with no one right answer. I strongly prefer deck stepped masts if they are properly engineered but more on that later.

Keel stepped masts:(better for big boats)
Advantages- It is easier to get proper support for a keel stepped mast right at the hull. In theory there are less side loads introduced into the deck and so is less likely to damage deck over time. Also if the rig is lost or damaged there is likely to be a bigger piece of rig left for a jury rig. On a racing boat it is easier to introduce pre-bend. Mast electrical connections occur below decks.

Disadvantages- If the mast has internal halyards (which I strongly recommend) then you always have water in your bilges. If the mast is not mechanically tied to the deck and keel, you stand a chance of springing the hull and bulkheads as the mast pushes down on the keel and the shrouds pull up and in on the hull. If you do loose a mast due you are more likely to sustain major deck damage. It is much harder to cut away a keel stepped mast and so the boat is more likely to be holed by its own rig. You have a big piece of aluminum passing through your cabin that you need to leave room around.

Deck stepped mast: (better all around)
Advantages: Easier to step and unstep. Simplier to tune. Does not bring water down below. Mast step and mast end is not in bilge and so less prone to electroysis damage.

Disadvantages: Harder to engineer. (see my opinion below). Electrical connections exposed to weather or concealed under mast. More likely to loose whole mast and hardware if mast is lost over the side.

IMHO masts should be deck stepped with the mast step over aluminum jack pole (king post) that has a welded top plate that can be through bolted through the deck into a moment connected bottom plate on the mast. This gives all of the advantages of both keel and deck stepped rigs.

Jeff

npronpro 11-16-2010 07:01 AM

I'm was thinking of replacing my wooden compression post with an aluminum jack pole (king post). How does one obtain/make up an aluminum jack pole and put it in?

I purchased two small hydraulic jacks from Sears and put them on both sides of the compression post, raised the 'ceiling' about an inch having removed the headliner/trim first. I then replaced a rotten rib in the bilge and put in some shims - this allowed me to strengthen the mast support without removing the mast (of course I had to loosen the stays and shrouds first and then tighten after lowering the jacks). Also had aluminum compression post plates made up to support the wooden compression post. This was not required but good backup procedure for wooden compression post. Lastly fiber glassed around mast on cabin top and re-painted gel coat with awlgrip. Very happy with repair. Pictures available.

Jeff_H 11-16-2010 07:32 AM

Quote:

Originally Posted by npronpro (Post 667232)
I'm thinking of replacing my wooden compression post with an aluminum jack pole (king post). How does one obtain/make up an aluminum jack pole and put it in?

Before you can have an aluminum jack-post fabricated, very careful measurements will be required. To do so, the mast needs to be removed so that you can take the measurements without any deflection in the deck. If there are any repairs which need to be made to the cabin top, or to the bearing at the keelson, these repairs should also be made before the measurements are taken. Then very carefully measurements need to be taken of the length of the post and the angles of the top and bottom plate in both fore and aft, and laterally. It might make sense to make up an accurate mock-up in wood to check your work, be certain that you can install it, and then you could give the mock-up to the fabricator as a pattern.

Depending on the size of the post and the thickness of the bearing plate, the connection between the post and the top and bottom bearing plates may need gussets to keep the plate from bending. These should be planned so that you are still able to get adequate bolting for the post. Lastly, you will want to either seal the post at the top and bottom or else have drains at the bottom if you chose to pass wires or otherwise have openings in the post.

Alternatively, you may also want to make all of the necessary repairs to the boat and then have the fabricator measure and build the post, making the fabricator responsible for producing the right product.

Jeff

AE28 11-16-2010 08:41 AM

We have a keel-stepped mast.

As Jeff mentions, we get water in the bilge every time it rains. Cannot think of any advantages to keel-stepped in our case.

omaho5 11-16-2010 08:56 AM

Although I prefer a keel step mast, Some boat builders do a great job on deck stepping.
Cape Dory has an aluminum "arch" running between the cabin and the interior liner in its deck stepped systems to support the mast. It works great.

JomsViking 11-16-2010 09:14 AM

Quote:

Originally Posted by AE28 (Post 667262)
We have a keel-stepped mast.

As Jeff mentions, we get water in the bilge every time it rains. Cannot think of any advantages to keel-stepped in our case.

A weep hole at deck level, and a little foam in the mast have solved that problem on numerous boats w. keel-stepped masts.

ccriders 11-16-2010 09:23 AM

When I was boat shopping I looked at several deck stepped designs and I have to say they were pretty sorry. (I was looking for an inexpensive 28 to 30foot boat). Deck compression, sagging deck because the "jack pole" was not adequately engineered, water intrusion from electrical connections, bulging partial bulkheads. Just a bunch of issues. I'm sure most of the problems occur because of differences between what the architect draws and the builder builds. Jeff H clearly states the advantages and disadvantages. You need to look closely at each boat and see how it was done in situ and go with your best choice. The negative about a big piece of aluminum in the cabin becomes a wash when a proper "jack pole" is installed.
I ended up with a pearson 28 with keel stepped mast and am happy with it. The mast is tucked into a nook in the head, seems massively strong and without internal halyards, the only water the mast sends to the bilge is from condensation. I pay close atttention to water accumulation in the bilge to avoid the electrtolysis mentioned above, and for other reasons.
Every boat is a compromise, isn't it?
John


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