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Discussion Starter · #1 ·
I've seen several boats with deck stepped masts instead of keel stepped. The keel stepped ones look sturdier, but hard to tell if that's the case. Aside from not having the "stripper pole" in the middle of the cabin, is there any other advantage or disadvantage of deck stepped masts?
Thanks!
 

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grumpy old man
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Both masts can be engineered for their application.
A deck stepped mast has "two pin ends".
A keel stepped mast has "one pin end and one fixed end"
Measured in moments of inertia the deck stepped mast will have to have a "stouter" section than the keel stepped mast. Reality is that with the available alu mast sections and the good practice of rounding up in mast calculations both applications will end up with the same section. In that case, the keel stepped mast will be "stronger" due to one fixed end, i.e. mast partners and mast step.

For me it comes down to:
If I wanted an offshore boat I'd like a keel stepped mast. That way if I am ever dismasted I will have a stump sticking up that I can use to rig a jury mast to get me home. A deck stepped mast will leave you nothing.

But this is an extreme way of looking at it.
The boat I owned for the last 15 years had a deck stepped mast. I was very happy with it. There was no water in the bilge from the mast.
 

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.....Aside from not having the "stripper pole" in the middle of the cabin......
Well, there are a few pros and cons for each, as mention above already. However, if you ever found yourself in a position to need a stripper pole down below, it would be pretty disappointing not to have one. :D
 

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Discussion Starter · #6 ·
Thanks. I've been researching Catalina 310's, but have not been on one yet. From the photos, it looks like it is deck stepped, unless the pole is enclosed within the forward birth bulkhead. In any case, we will be coastal cruisers and weekend/day sailors, so not too worried about being caught out on the "big blue" dismasted, but it is a valid consideration.

I didn't consider the leaking potential of the cutout. I did however, consider the potential need of the "stripper pole", but my wife just rolled her eyes!
 

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Guess what? When I saw this thread, I said to myself, "I don't know the answer, but a guy like Bob Perry would". And he was first to respond. Give me a gold star!
 

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Guess what? When I saw this thread, I said to myself, "I don't know the answer, but a guy like Bob Perry would". And he was first to respond. Give me a gold star!
Yet another issue/question Bob has already addressed in detail in his book...

In a perfect world, more folks out there would read it...

:))
 

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Not all manufacturers provided an adequate deck structure and deck to keel support for a deck stepped mast, so look carefully at any boat you are considering for deck compression and deck deflection. Especially if the boat has been aggressively raced.
John
 

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Most Catalina 310's I've seen have in mast furling which are all deck stepped aren't they? I really don't know, just assumed there are no keel stepped furling masts ?
Good news is that deck stepped boats have a compression post in the cabin so stripper pole is included.
 

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Old soul
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Each have their advantages and disadvantages, much like most boat choices it seems. Get a well designed, well built boat and either would be fine.

BTW, ours is deck stepped, but alas, no stripper pole. Our compression post is a solid timber of teak. Try as I might, I can't convince my beautiful partner to give it a try :-(


Why go fast, when you can go slow
 

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The issue of 'leakage' with keel stepped mast is not so much leakage around the deck/mast partners - there are many ways to seal that; the more difficult and unavoidable water is what gets into the inside of the mast through all the halyard exit/entry points and runs into the boat that way. Depending on mast design and configuration this water ingress can be considerable.

I'm leaning towards deck stepped should there be a 'next boat'...
 
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Mermaid Hunter
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I've seen several boats with deck stepped masts instead of keel stepped. The keel stepped ones look sturdier, but hard to tell if that's the case. Aside from not having the "stripper pole" in the middle of the cabin, is there any other advantage or disadvantage of deck stepped masts?
As a practical matter there is no particular structural advantage or disadvantage. I think stowing your spinnaker pole on deck instead of on the mast (where mine is *grin*) would have a greater positive effect on survivability and self-sufficiency after a casualty.

As Bob Perry notes, keel-stepped masts are modeled as having a fixed end while deck-stepped masts are modeled as pinned. On larger offshore boats the reality is that the keel-stepped boats have more flexibility at the coach roof than a true fixed end would indicate, and deck-stepped masts have more resistance to rotation at the step than a pinned end would indicate. As a practical matter, Mr. Perry is spot on that naval architects will always round up to the next standard available production section, and if the rounding is "too close" (a judgment call) will round up another step. On top of that you may go bigger yet to keep roller furling straight in a pre-bent mast and have room for conduit for all the goodies aloft. Ultimately, a finite element analysis provides better assessments than the simpler pinned/fixed calculations. Given the other considerations it just isn't worth the effort for a few more decimal points of accuracy.

Thanks a lot Jon but let me adjust that:
In a perfect world more people would BUY it.
I am still about $450 of making back the advance on royalties!
I'm hoping to sell the movie rights for BIG money.
As a degreed naval architect (Webb '82) I looked forward to Mr. Perry's book with eagerness. I pre-ordered (from Amazon I think) and read it carefully. I enjoyed it. I didn't necessarily agree with all his design decisions (I have sailed a lot of Perry boats on delivery) but reasonable and competent people can look at the same information and come to different conclusions based on priorities and experience. I never lose sight of the fact that there are a lot more Perry-designed boats on the water than Skolnick-designed ships, or that boats and ships are quite different beasts.

I highly recommend Mr. Perry's book to anyone interested in what leads to the boats we choose to purchase and sail. You don't need to be particularly technical to gain a lot of knowledge from it.

The coffee table format does make storage on the boat a tad awkward. I keep my copy in the bottom of an odd-shaped locker instead of a book shelf.

On behalf of my alma mater, I also appreciate Mr. Perry's support to the Webb winter work program. Is it too late for me to gofer in your office?
 

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grumpy old man
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knut:
There are two ways you can get a signed copy of my book.

The preferred way is for you to bring a copy of the book up to my beach shack in a brand new, red, Jaguar convertible. You leave the Jag and I sign the book. Easy squeazy.

Or you can mail me a copy of the book with return postage included. I'll sign and personalize the book and send it back to you.
 

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grumpy old man
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Auspicious:
Come on up. I have some organizing of archives you can do. Not sure they taught you that at Webb but we can figure it out together.

My files are a mess since I moved the office. Can you file? I don't file. I pile.

Many thanks for the kind words.
 

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Have had deck stepped and currently keel stepped boats. Just wondering if the hydraulic backstay effects them differently. Would think with a fixed end and a longer section for the deck stepped even though there will be little or no movement at deck level the keel stepped will bend more with less force.
Agree that keel stepped means more water in bilge. Note that sailing or on anchor/mooring this is less of an issue. The sail track is aft so out of the wind/weather and the halyard exits on the sides are some what parallel to wind direction usually. It is a more significant when in a slip unless wind right off your bow.
Have seen folks fill the section just above deck with foam and place a drainage hole above the foamed section. Having a small amount of fresh water in your bilge seems no reason to be concerned to me. I like having the light for the low level bilge go off every once in awhile. Nice to know it works even though I turn the high and low bilge pumps on manually before leaving my port to check them that's different then knowing the float switches work.
 
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