Supporting the Main Mast

Three Solutions for the Mariner 31/32

From the top: A) Bruce Allen's version - B) Randall Reeves' version - C) A digram from "Maranatha" a 1979 M32 Made in California.

Edited by Bill Kranidis

Bruce Allen and Randall Reeves

October 2009



One feature of the Mariner ketch is its deck stepped masts.  Advantages aside, and even in the best built boats, this installation can cause compression issues as the boat ages, evidence of which in Mariners is separation of the supporting deck beam from its knee (vertically) or the bulkhead (horizontally) or both.  Below are two main mast support solutions for the Mariner 31/32.




A) T-Flange Beam

Gitana Vela, M31

Hull 95

Bruce Allen



Gitana Vela has a T-Flange beam of stainless steel inserted directly under the main mast supporting beam that runs the width of the boat.  This upgrade was performed by a previous owner, but was a professional job and, as Bruce report, it has cured the compressions issues on the boat entirely.


Image 1


The T-Flange is fabricated out of two pieces of 304 stainless bar stock, one vertically and the other horizontally positioned and both formed to the curvature of the deck beam.  The above photograph looks toward the bow.  The original vinyl liner on the coach roof has been removed in preparation for paint.




The two pieces of the T-Flange are arranged as follows: 


Image 2


1) A vertical piece of ¼ inch stock is cut to run the entire width of the cabin just forward of the head/closet bulkheads and is shaped to fit to the curvature of the main support structure.  The port side is pictured here.



Image 3


2) A horizontally fashioned piece of 3/8ths inch stock is cut to fit the “visible” length of the original mast support beam; that is, it does not extend inside the port closet or the head, but does extend to both cabin sides in the V-berth.  Here the entire T-Flange assembly has been removed and is visible from its top side, which reveals its pattern.  The “burn” marks down the middle of the piece are where the vertical piece has been welded on from underneath. 




Image 4



Fasteners are run vertically into the mast support beam and horizontally into the bulkheads and knees. 



Image 5


Two machine screws fasten the flange to the forward side of the head bulkhead and knee (starboard), seen here from inside the head.  One fastener is used on the port side (below photo).


Image 6




Image 7


Type 316 stainless is used in most marine applications, and though it is very corrosion resistant it may be a little more malleable under load than is appropriate for heavy duty installations like the above.  Thus, this T Flange was made out of the stiffer and stronger type 304 stainless.  Because this is an interior installation, the reduction in corrosion resistance of 304 should have no effect.




B) Compression Post

Murre, M31

Hull 150

Randall Reeves



The design for this solution came from Chuck who owns Adalente, an M32, and who was kind enough to let me copy it exactly.  A few of the following photos show the post in the process of being installed on Murre and so are missing some of the finishing touches, which will be mentioned in the text.


Image 8


Most notably, the post is designed to be removable, and by extension, adjustable (or vice versa—I’ve never been sure).  This turned out to be more important than I might have initially judged; I first installed the post when the masts were in and the support structure under load, but I moved and placed it more permanently when the sticks were out a year or two later.


The rod is made of 1 ½ inch diameter stainless steel tubing with 3/16 inch wall and a length of 5 feet 6 inches.  Left bare, it can be bloody cold against the warm thighs of one exiting the V berth bunk to visit the head.  One good scream from the girlfriend at 3 o’clock in the morning was enough to warrant a half day of half hitching.




Image 9


A 1 inch hex nut is welded to the top of the post.  Into this fits a 1 inch stud about 8 inches long that’s welded to a top plate.  Turning the post via the hex nut adjusts the overall height.


Two pieces of teak framing tacked to the deck beam next to the long side of the top plate (not pictured) keep the top plate in place.



Image 10


In order to make it easier to access the V-Berth, I’ve positioned the post a few inches to starboard of center. 



Image 11


The post sits on a 5 inch by 5 inch steel pad by way of a 1 inch nipple welded to its base, which allows the post to swivel when being adjusted.


And the whole post assembly sits atop a piece of 1 inch Mahogany that runs the width of the area.  Unfortunately this pad covers part of both floor-board hatches.  I shortened the aftermost hatch and the other I knocked new out of left-over Mahogany.  This installation also blocks closed the head-to-Vberth door.  We never use it, so this is no great loss.



Image 12


A fiberglass frame (difficult to see here) supports the cabin sole under and forward of the post base, so ensuring all the post’s pressure is transmitted to the keel requires blocking from underneath aft of this frame.


Here two blocks are being fitted but are not yet glassed in place.



Image 13


The fabricator wrote up the following notes for his crew, included here as a concise summary:


“Fabricate -1- Mast Support Rod as per drawing out of 1 ½” diameter stainless steel tubing with 3/16” wall and 5’ 6” Long with 1” standard threaded hex nut on one end welded in place.  Weld lug in other end turned down to 1” diameter by 3/8” long.  Furnish -1- 3/8” thick top plate with dimensions 3” by 5” and weld 1” diameter by 8” long stainless steel stud to it.  Furnish -1- 3/8th thick bottom plate with dimensions 5” by 5” and drill center 1” diameter for plug to swivel.”

C) Mainmast Support on "Maranatha" a 1979 M32 Made In California by Clair Oberly (after operations were moved there).