Mast Step continued...

Where was I?  Mast step.  Right.  As I may have mentioned in prior posts Creeky came with a lot of important parts and loads of potential, but very little in the way of instructions.  Most of the time this is great because I get to use my imagination and come up with creative engineering solutions while double-checking my work with some trusted references.  However, designing and building a mast step is one of the handful of key components of boatbuilding that didn't really come up in the textbooks I have.  There weren't even many online arguments about the best way to build one in the forums I usually poke around in.  It's either assumed that this was already built into whatever structure sits below the floor or that the clever reader has the requisite knowledge to scratch something out on the back of an envelope without giving it much thought.

I took it to be slightly more complicated than that though, and decided to over-engineer it to a sufficient level of mental comfort.  Even now as I look at the mast sitting on top of the step I have that little itching question in the back of my mind.  "Could I have built it just a little bit stronger?"  What I think some people take for granted about the mast step is the amount of force it must withstand.  Even at rest the downward force on the mast step is tremendous.  Consider the following:

Approximate extruded aluminum mast section:
Dimensions: ~12in x 6in
Wall thickness: ~.3 in
Weight/ft: 15+ lbs (taking internal roller furling structure into account)
Length: 62 ft
Overall weight = 15 x 62 = 930 lbs

Now add in all nine 3/8in 1x19 stainless steel wire rope stays, each with a breaking strength of ~17,600lbs, driving the mast into the step like several giant compound bows all at once.  Assuming they are tensioned at 1/10 of their breaking strength (total guess), that would make:

9 x 17,600 = 158,400/10 = 15,840 lbs on top of the mast weight.

So at rest we may be looking at almost 17,000 lbs of force directly onto the mast step!  That doesn't even begin to take into account the myriad variables that can't be calculated or planned for, so there needs to be a considerable safety factor on top of that.  No problem...

The basic premise of a mast step is that it is a structure that distributes the load imparted by the mast to a larger section of the hull and keel.  I decided to build a step that would be strong enough to withstand the necessary loads but also allow for fore/aft adjustment of the mast foot on top of it.  This was primarily to give me a little room for error when cutting the hole in the deck for the mast, but could theoretically allow me to give the mast a little bit of rake if I wanted.  

Lining up height of mast step

The basic design of the step was to have four 2 x 6 in pieces of mahogany, each ~3 feet long going from port to starboard, with a 1/2 in thick, 6 in wide, 18 in long piece of 304L stainless steel going fore/aft.  This would be secured at either end and underneath to 1/4 in angle steel for extra sturdiness, and thoroughly bonded and fiberglassed to the top of the keel. 

Bonding

 I used a WWII era Bridgeport mill to fabricate the stainless pieces.  I could write about that machine for days, and I barely know how to use it...

Drilling

Milling

And more!

 Below you can see how the midsection of the stainless plate is attached to the mahogany bulkheads (I wanted to call these stringers, but my friend Nick corrected me and said that stringers go fore/aft and bulkheads go starrboard/port).

The bolts are counter-sunk so that the step plate can slide on top easily.

Almost done.

Finished product.

Still, could it be stronger???

Minor update - mast step

I had given up on the idea of being able to adjust the position of the mast step with the mast in place until Charlie suggested cutting a small access hole in the foot of the mast. I was nervous at first, but it seems like a solid move. 

Boom!

Chainplates start to take form

New dock lines

I bought new 3 strand nylon 3/4" dock line, which I had spliced by a guy at the store I bought it from. When I got it back I saw that he had finished the splices and cut ends with electrical tape. Not very yar...

I removed the electrical tape and melted the bejesus out of the splices and ends to ensure they would be extra rugged. 

Next, I needed to cover the melted parts. Since I didn't have the time or energy to learn how to properly whip the splices, I decided to use an easier alternative after seeing a product called dip-whip. On a nearby shelf was a similar product called plasti-dip that had three times the volume for a third of the price. Sold. 

Here I am masking off the places that I will apply the plasti-dip to. 

Here are the ends post dipping. 

And the finished product!  I applied 3 coats in total. 

I have to admit that i was pretty skeptical about the whole process and whether the plasti-dip was really sufficient for the application. However, after a few coats and sufficient drying time the stuff feels really tough. Overall I am very pleased with the results. Time will tell how well the stuff works though. 

Yacht Design 101 - About exactly as hard as you would think it is

Sometimes I am reminded of the fact that I'm not just working on building a funny little quirky floating apartment, but a rather sophisticated piece of engineering wizardry.  Due to the limited amount of information available on Creekmore Sailboats, and mine in particular, it's not just as simple as assembly.  At this stage of the game there is actually quite a bit of serious calculating, design, and fabrication required before I can take 'ol Creeky out for a sail.  This is primarily in the design of the standing and running rigging (the cables that attach to the mast and the lines/hardware that control the sails).  While I could farm out the whole process to a naval architect or similar expert, it would be much more expensive than I can afford at the moment.  The cost of the rigging itself this summer will be more than enough to keep me broke.  I feel that it will be a huge benefit to fully understand the forces acting on the boat in any given situation.  This will help me to be more confident in the mechanics of the boat; but will also give me the knowledge to deal with any rigging failures down the line where I might not have a knowledgeable, English-speaking naval architect on hand.

So I'm doing the math myself.  The two books I am buried in right now are "The Complete Rigger's Apprentice" by Brion Toss, and "Principles of Yacht Design" by Lars Larsson and Rolf E. Eliasson.  Pretty light reading...

While I hope to to the bulk of the planning myself I will definitely get some input from more knowledgeable folks before trusting my assumptions and calculations.  My friend Jesse had a great idea: get in touch with a naval architecture professor and see if they could make it a student project.  Just waiting for responses now.  Thanks for the idea Jesse!

Another reason I didn't want to spend a bunch of money on a naval architect is that many of the dimensions that could be designed are already fixed.  The mast is 62', the boom is 18', the hull a'int changing at this point, and I already have all the sails.  There's also about 10,000 lbs of lead ballast epoxied into the keel.  My hope is that the bow will settle down a bit when the mast is installed, but if it doesn't I'm just going to have to deal with it and maybe add some more ballast towards the bow.  Even if I went with a naval architect and they told me they would do things differently, like add a mizen mast, I still wouldn't.  I am going to build the boat as Henry originally designed it, or as close as possible given the information I have.  I'm getting there.

One thing that has helped is the layout drawing of the hull with a view from above and from the side (down to the waterline).  This doesn't include the mast, rigging, or the keel, but I realized it was in 1/20 scale and built a 3D model using Google Sketchup.  So far I've just built in the more basic dimensions, but eventually I plan to model the entire boat.  For anyone that uses Google Sketchup, I shared the model in the 3D warehouse.  Search for "Creekmore 45."

Just playing around with the Google Layout rendering

Top view

This will be expanded on soon

Notice the boom angle.  That was specified in the notes I have.

Another side view

Basic, but not too shabby