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Building the
Slo-mo-shuns

This story is a reprint of an article Anchor wrote
for a book called "US Boats 1" in 1953

Slo-mo IV at Jensens: In the process of
finding out if and where that big Allison
engine will fit where Anchor wants it!

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The Building of Slo-mo-shun IV & V
By: Anchor Jensen

Reprinted, courtesy of "US Boats1" 1953

There's an apocryphal tale about the mountaineer who scaled the highest peak man had ever conquered and got home safety to tell his wife about it. "Now that you've done that," said the sweet little woman, "what do you do next?"

We recount this story in a book about boats because the following article is by and (somewhat) about a man who happens to be a skier and mountaineer, as well as a boatman, and because he found himself in somewhat the same situation as the man in the story. Anchor Jensen had the answer to "what do you do next," however. Having built the first Slo-Mo-Shun he quite logically went ahead and built another. When you're out in front of the field and still try to better your own best efforts, you're really in there pitching--if we may mix a baseball metaphor with boating and mountaineering!

Anchor Jensen grew up with boats, being the son of Tony Jensen, founder of the Jensen Motor-Boat Company of Seattle. Even as a lad, he took an active part in the business and, when he went off to school, took an engineering course at Seattle's Washington School of Engineering. Came the war, and Mr. Jensen went to Great Lakes Naval Training Center Basic Engineering School, from which he graduated with honors-and then served in the U. S. Navy on the USS Iowa and USS Belleau Wood. Soon alter V-Day. Mr. Jensen was back to his true love, high-speed boats. He's been building them ever since, and is now manager of the boat company where he spent his childhood. Both Slo-Mo-Shuns IV and V were built under his supervision and active participation. Mr. Jensen is a member of the Seattle Yacht Club, Corinthian Yacht Club, A.P.B.A., and the Seattle Mountaineers.
US BOAT

I have been asked to write an article on the building of Slo-Mo-Shuns IV and V. To cramp a lifetime ambition into such a short article is impossible, however, here are some of the highlights:

At the start, Mr. S. S. Sayres, the owner, summed it up in a very few words by saying: "I want a boat to win the Gold Cup, Harmsworth Race and to set the mile straightaway world record with a budget of so much." We lived up to his wishes and succeeded setting records in all categories including exceeding the budget.

A boat builder, carpenter or contractor usually has plans, building codes and specifications to work with. Materials are stressed with great safety factors and a relatively large margin of latitude is permissible.


We had nothing to guide us
except to look at what
was running and
its good or bad points.

In the case of the Slo-Mo-Shuns it was different. We had nothing to guide us except to look at what was running and its good or bad points. We had no tables for hull stress nor any data to guide us for the over one hundred miles per hour class. Thus we took on the job of building the vessels with only ideas scattered in the minds of three people: Ted Jones, S. S. Sayres and myself as the builder, had the last vote, for it was my job to collect these ideas and develop them into final results.

It was decided that a three-point hull similar to the propeller riding California boats was our answer in regard to hull-form. To make it strong and light, mindful of the budget, we chose wood for construction, with Dural aluminum riding surfaces. Each piece of wood to be used for battens, frames and so on was given a break test on the part that was cut off as waste, and was carefully checked for grain run-out. All metal parts and welds were magnafluxed, X-rayed, or zyglowed to check for flaws. Of special interest was the vast use of welded high carbon steels in the rudders and steering gear and struts. We devised a welding procedure which most experts would frown upon, although the results have been most satisfactory.

The hull on Slo-Mo-Shun IV is 1/2' thick Tanguile mahogany laid up in five plys, with each ply laid 45' off the center of the sheet alternately. Slo-Mo-Shun V is the same Iexcept for 7/16" thickness. Decking is Tanguile mahagony 3/16' thick over 5/8" square oak battens on 6"centers, fastened to laminated spruce deck beams. The frames are 7/8" by 3" oak, half, lapped at the chines with 1/4" plywood gussets glued on both sides. The chines are oak 1 ½" square, glued and, bolted to frames. The bottom battens are 7/8" x 1 ¼" oak and are piled on to the frames without notching. Engine beds are made of 1 1/4" spruce fastened with Dural aluminum T sections to the frames. Thus we have four fore and aft spars, two engine beds and both vertical sides of the hull extending from transom to none-trip forward. Transversely, the frames are spaced at 18" centers with 9" centers at points of localized stress. The fore and aft bottom battens make again in form, a truss with the engine stringers, thus giving us an equivalent member of 20" in section. Transversely we gain a truss section in the frames and planking making its section 4-3/4". In this way by placing each member for its job and forming truss sections we have gained light weight and strength of sections. The engine beds are reinforced with Dural formers or bulkheads transversely and fore and aft with long deep angles of Dural aluminum to distribute the major concentrated load. The engine is called upon for two purposes: to form the top transverse chord of a truss and to supply power to drive the hull.

"Why did you do this
or that or why did you
not do it this or that way."

I have had many people ask me, "Why did you do this or that or why did you not do it this or that way." To answer such questions you only have to explain the purpose of the installation, the job it does and its relative cost, to make any other way to seem impractical. We have even incorporated the skid fins in-to a structural member of the hull. Thus any part that was necessary and could offer structural strength was made to perform multiple jobs.

I am always mindful of the old saying that what goes up must come down which has a rather parallel effect on high-speed boats, for added weight although having not too much effect on top speed-has two bad effects: one on acceleration and one on tearing up the hull structure. We played with several ideas which seemed good at the time (but back fired later) which meant additional work of correction. However, as a whole, careful planning and organization has produced what we desired and has been relatively dependable.

We increased the shaft diameter, beefed up the steering, changed struts, added more HP and increased the gasoline capacity in both boats as the demand warranted it. Naturally we ran into problems which one normally expects in any experimental endeavor. To name only a few: outer plywood planking, struts, rudder and steering gear, step-up gear and countless others. I wanted transverse strength in the plywood which meant a special lay in the plywood of a long fibred wood and hot press process glued seam. Lots of string pulling and discussions with Elliott Bay Lumber Co. in Seattle finally produced what we wanted at a reasonable price. The firm cooperated with us to manufacture a plywood that would flex and still have our limits of transverse strength.
Nelson Iron 'Works in Seattle produced the drop forgings of 4130 steel which formed struts and rudders to our specifications. After hours of machining and grinding by Bowers Machine Co. in Seattle a billet of 105 lb. was reduced to 40 lb. and we had a finished main strut. 'Western Gear Works in Seattle picked up the ball on the gear box, working along with our theories. They engineered one superior to anything on the market. 'We even had to devise a new key-way cutting for propeller shafts. Countless other problems came up as the speed increased. To build monsters like the Slo-Mo-Shuns would not mean anything if they could not produce results and this in turn reflects on the designer and builder also as well as the crew and drivers. Countless hours of testing and maintenance have been put into the boats with the idea of improving the product and learning.

I think we have reached an ultimate in design and construction in this class of boats and along with displacement hulls like Miss Pepsi we will have to dig into the grab bag for new ideas. On the straightaway course we will have to cope with the jet driven boats because they have an edge that cannot be passed over lightly. However, I feel that they approached the idea from the wrong angle in trying to produce a 19th century boat with a 20th century power plant. The crack pot jet boats which have been devised so far are casting a bad light on the jet power plants and brand them as man killers. I hope the public realizes that it is not the jet plant but the design and construction of the hull that makes them unstable. In summarizing, the building of the Slo-Mo-Shuns has been a challenge, but has yielded satisfying rewards for the long hours, hard work and many disappointments. The boats are a tribute to our workmen who went beyond mere line of duty by working throughout many nights in emergencies and offering their services as crew members.

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