We’ve finished our the basic construction of our boom and will put it aside until we’ve completed fabricating the sail track and casting all the fittings that go onto the boom.

As shown on the accompanying sketch, the original boom was fabricated metal, with steel plates riveted over rings and angle iron stringers. Rivets were ground flush so in our scale they would not appear. Much of the boom was a “straight stick” of 21″ diameter; with common upper and lower plates (shown as B-1 which were 14″ long and rolled half round). It would appear that this simplified construction. The top halves overlapped the bottom halves, while the ends were butt-jointed together and fastened inside and out to straps with rivets. As mentioned, these plates were also riveted to rings and stringers. I imagine that they must have made a jig or tool to buck the inside end of the rivet, but would appreciate any insight from our readers. I cannot imagine there was anyone small enough to fit inside these rings and the 21″ diameter pipe! Typically, there were four rings equally spaced 3’6″ inside each section of plate and plates were jointed half-way between adjoining rings. Top and bottom plates were alternatively arranged to minimize weak points.

We should note that mid-May 1903 after a month of sailing, NGH added 3′ to the boom ( and 18″ to the gaff) and had the sails recut.

We built our boom of “Lawton Steel” named for our chief woodworker; hence wood made to look like steel. We laminated two 20′ long douglas fir 1″ x 4″ planks together to make a top and bottom. From a fifth plank we cut two 1/2″ strips which we glued a little proud of the edges of the second lift of the bottom half. Thus, the final shape would be of five planks and almost square in profile.

We routed out the insides of each half to give us walls of 1/2″ in thickness, which we believe to be strong enough but as light as possible. After shellacking the inside hollow portion we glued the halves together. We marked lines on the square profile to represent edges for an octagon and then planed these to perfect octagonal profile. Next, we knocked of these edges and sanded until we were nearly round. At this point we created our overlapped upper plate joints with thin strips of basswood, filling in as necessary with Bondo. Thin basswood strips were also added to represent the butt joint straps. We painted our boom with several coats of primer, sanding between each coat until we achieved a metallic finish.

We’ll put on a final coat of paint, but for now our boom hangs in its rack awaiting completion of the many cast fittings that’ll be attached later.

Sketch of Boom

Boom being sanded to look like metal

Boom after plating seams added

Boom after plating seams added

Boom rounded to shape

Tim does final sanding on boom

Keith planing octagon shape to boom

Keith knocks corners off the octagon

Squared boom is made into an octagon

Bill takes Squared boom to an octagon

Hollow halves glued together

Ready to be glued together

Insides have been shellacked

Bill Routs out other half of boom

Routing out hollow boom half

Several people have recently asked how the telescoping topmast worked. 8’4″ of the 58’3″ Sitka spruce topmast resided in the mast when fully erected. I have enclosed a sketch of how all this worked. A sheave at the butt of the topmast and sheave in the mast provided the mechanical advantage for the 330′ long 3/8″ diameter P.S. 19 steel topmast heel rope. The mast was fabricated from rolled steel plates riveted over rings and stringers. The top 24’8″ of the mast was tapered so the topmast was kept in place with lower and upper bearing rings. A fid resting on a ledge in the mast and kept the topmast in its erected position. Interestingly, the fid slot in the topmast was through the parabolic hollow section of the topmast, rather than through the solid portion. I wonder if this parabolic shape help better spread the load for the hollow topmast?

I also enclose pictures of the team shaping the topmast into its 13″ scale diameter. These pictures go with the earlier topmast posting and complete the basic construction of the topmast.

telescoping topmast operation

Getting ready to plane square topmast into octogon 1

Octogon shape marked out and being planed by Bill

Bill planes topmast to octogon shape

Topmast brought to round shape by planing edges and then sanding with long box

Topsail club after sanding

We’ve discussed the topmast before, but it is time for an update. You’ll notice on the topmast sketch ( photo 1) that this spar is not the usual barrel stave lay up. That may be because it is a constant 13″ o.d. its full length. We decided to follow Capt. Nat’s drawing as best we could to gain insights into his methodology. It turns out that it really is an easier approach than the barrel stave approach! We also found that working in sitka rather than Douglas fir is easier but the saw dust is much worse.

RELIANCE broke her topmast during a Defenders’ trial race in June, 1903, and the mast was changed from douglas fir to sitka. While douglas fir is stronger, sitka is lighter and Iselin commented that the 2nd topmast was 23% lighter than the original. This was done to put less pressure on the fid which held the topmast in place. (You’ll note in the drawing that the fid actually pierces the topmast in the hollowed out portion of the topmast.)

The topmast is hollowed out to a diameter of 9″ at the ends and 7″ in the middle; again Capt. Nat was taking out all weight he could while maintaining required strength.

The Topmast was a telescoping topmast fitting within the fabricated steel mast, and as you see there is a heel rope sheave at the bottom of the topmast. One end of the wire heel mast rope was fastened inside at the top of the mast, then lead down through the heel rope sheave and up to another sheave mounted at the top of the mast. The wire was then lead down to deck level for hoisting and lowering the mast. The above referenced fid kept the topmast in its erected position. There were slots in the mast and topmast and a shelf inside the mast on which the fid rested.

Photo (2) shows us first planing edges of our block of sitka flat, then ripping our eight scale 5″ x 5″ planks which were then glued into pairs for each side. We then routed out quarter round scale 7″ diameter hollow with taper to 9″ hollow at each end for each side. We used a ramp in the middle to raise the router from 9″ depth to 7″ depth. Afterward, each side was mitered with 45 degree edges (4, 5).

We first attempted a simple glue-up jig approach but found it unwieldy, so we quickly wiped off the glue and with all-hands on deck, including Kyle who we borrowed from the mentoring program, built our second jig and glued the four sides together. This second jig had ledges that conformed the the shape of the sides as shown in the sketch (photo 1) while keeping required pressure on the sides and then the top when finally closed up. As you can see in photo it was a mad dash to recover from the first attempt and to get all four sides glued at once!

Photos show the topmast sides curing in the jig and then after being removed. Drawings show us planing off the excess on each side to get our square shape. Note the templates in the foreground which we used to get the octagonal outline at each end and along the sides, and the round template for final shape. The next pictures show us planing our topmast into octagonal shape. Each set of edges we take off gets us closer to roundness. Finally we were ready to use our long board to sand the topmast round.

Still to go are steps final sanding, shellacking and varnishing of the barrel, shaping the cone at the top and adding the truck, sheaves and fid slot, but I’ll save these for a later post.

Topmast Sketch

Planning edge of topmast planks

Cutting 45 angle to topmast sides

Four sides ready for glue up

First attempt at glue up

Building jig for 2nd attempt

Close up of jig and glued up topmast

All hands mad dash to glue up all four sides in jig

Topmast curing in its jig

Glued up Topmast popped out of jig

Topmast in its cradle with templates in foreground