Cockpit and Motor Mount Measurements and Details

A reader and fellow Tiki 26 builder wrote the other day to request some measurements on my cockpit clearance above the waterline and the depth of the prop of the Nissan Extra-Long Shaft 6hp outboard.  Because the cockpit is slightly deeper than the 9 inches shown on the plans, he was concerned about wave tops slamming the bottom, and also wanted to make sure the prop was deep enough to avoid cavitation in a chop.  I had to reinstall the cockpit the other day to make some other measurements anyway, so I shot these photos showing the requested dimensions.  I made up for the two-inch extra cockpit depth somewhat by making my beam mounting blocks on the deck thicker by almost that amount.   I don't think clearance will be an issue, and with the extra-long 25-inch shaft, the motor can be mounted high in the cockpit to protect it, yet it will still reach deep enough so that it will almost touch bottom if the keels of the hulls do.  This first shot shows the depth of the cockpit hanging below the aft crossbeam:

Here you can see can see the depth of the prop, again measured from the bottom of the aft crossbeam:

The bottom edge of this piece of 2 x 4 lumber is in line with the bottoms of the keels adjacent to the motor.  As you can see, the prop can't hit bottom before the boat runs aground, as the deepest part of the keels are slightly forward anyway, in the midships portion of the hulls:

This last shot shows the 2 x 4 at the approximate average load waterline.  The bottom paint is probably 3-inches above the true waterline to allow for heavy loading at the start of a voyage.  As you can see, with the extra-long shaft, the prop is unlikely to come out of the water in anything but the worst conditions:

Test Fitting the Cockpit

After finishing the forward decks, I completed the basic assembly of the cockpit box and temporarily fitted some stringers on the ends so I could hang it from the beams and check the alignment and fit of everything.

 

This is just the basic center section of the cockpit, built to plans with a foam-sandwich floor.  This floor is lightweight and incredibly stiff, with no signs of flexing when walked on.  Hanging it in place allowed me to scribe an accurate line on the inboard sides of the cabins, for the placement of the rails that will support the outboard edges of the seats.  There is clearance on either side of the 4-foot wide cockpit box to accommodate a 12-inch wide under seat storage box on each side.  These will be dry storage areas closed by the hinged seats, and will provide a place for the batteries and other essential gear. 

The extra-long-shaft Nissan outboard sits high and dry in the cockpit well, where it will be well-protected and easily accessible.

The 25-inch shaft length makes it possible to mount it this high and still have the prop deep enough to minimize cavitation in choppy conditions.  You can see here that it will be well under water, yet not deep enough to strike the bottom before the hulls do:

After making sure this fit was good, I then cut out the opening in the aft end of the cockpit that allows the motor to be tilted clear of the water when it is not needed, which hopefully, will be most of the time.

 

Now the cockpit is back in the shed on saw horses for all the finish work on the fillets and glassing, as well as construction of the seat boxes.  Like every other part of this project, the assembly of the parts is a small percentage of the real work that has to be done before the parts are finished and painted. 

Net Beam, Anchor Roller, Cockpit, Motor Mount and Deck Mock-Up

The weather has been spectacular here in Mississippi since I moved my hulls out of the shed.  They haven't seen a drop of rain so far, and the humidity has been low and the temperature just right for epoxy to cure.  I'm working on a lot of miscellaneous projects that had to wait until the boat was assembled for correct measurements and final decisions on details.  One of these projects included mocking up the cockpit by temporarily hanging the side panels in the space between the mast beam and the aft beam.  I was then able to screw a temporary 2 x 4 in place to represent the height and fore and aft placement of the motor mount, so I could check clearances and make sure it would be the right depth in the water when down and still tilt up high enough clear the surface when sailing.  The motor I'll be using is a Nissan 6HP Extra-Long Shaft 4-Stroke. 

I think it's going to work out fine in the space shown for the motor well in cockpit drawing in the plans.  Because of the 25-inch shaft, I can mount it a bit higher, which will help prevent it from drowning out in big waves.  It will still be pretty low overall in relation to the top of the aft beam, as you can see here:

The 25-inch shaft will keep the prop deep in the water, with cavitation unlikely.  Mounting it forward of the aft beam will also help with this and with proper weight distribution.  The board laying across the skids that the hulls are resting on in front of the prop shows that the prop can't hit bottom before the hulls do. 

I've also designed and built the aft net beam in the past few days.  I scrapped the idea of using the aluminum pole I had for this, as a wood-composite beam will be easier to mount things to and to finish in a way that matches the boat.  I used a V-shaped lamination for the bottom, fit into notches cut in the stern post.  The other board is the inner top plate, beveled to fit into the V.

Here is the next assembly step, putting the inner top plate in place with epoxy.

This  view of the unfinished end shows the final cross-section of the beam.  Built of Doug fir, it's plenty strong and stiff while still lightweight because of the hollow area.  The piece of wood on the forward edge that stops at the inside of the sternpost is a teak trampoline lashing rail that will be drilled on 3-inch centers for the aft tramp lacing.  I'm using teak for all the  lashing rails as the holes will be exposed to the weather and most other woods would rot in this use. The sharp edges of the beam corners will get a smooth radius and then the entire beam will be sheathed in fiberglass cloth.

Here's view looking aft to show how the beam fits.  The triangular design with the low, flat top will allow plenty of clearance for the tillers.  There's a lot of usable space back there between the sterns and the aft beam.  I can't imagine not having a net beam to take advantage of it.  Mine will have a drop-down ladder in the center with tramps to either side. 

Anchor handling and storage is often overlooked in the building phase of these boats, but any cruising boat, no matter how simple, relies on good ground tackle, and that ground tackle must be accessible and easy to handle.  To that end, I've built a custom anchor roller for the forward beam that nicely accommodates my 22 lb. Delta plow anchor.  Anchors in this configuration are difficult to stow anywhere but on a roller, as they are bulky, awkward and take up too much space inside lockers.  The roller housing is assembled here for fit, but will be removed for finishing before it is then filleted and glassed onto the beam. 

Here's the anchor, salvaged from my previous boat, a much heavier 26-foot monohull.  The Delta should be more than adequate as the main anchor on the Tiki.  If I were buying a new one, I would probably go with the highly-regarded Rocna design.  As it is, I have this one, as well as a smaller CQR and a large Danforth.  All three will be on board with appropriate rodes.  At the top of the beam, there will be a teak block to receive the shank and hold it in position, and a cleat to secure it with a short line through the forward eye. 

Another big project will be building the slatted deck forward, between the mast beam and the forward beam.  I've decided to go this route in lieu of a trampoline, as it is so much better to work on and will last longer.  It will also cost about the same or less, as I have ordered locally-grown select-grade southern bald cypress for the material.  I considered teak, like David used on his Tiki 30 forward deck, but prices have really gone through the roof, especially for what little teak is available in my area.  The cypress will be lighter weight anyway, and should last a long time with care and proper construction.  Below, I have mocked up some of the longitudinal stringers out of scrap wood just to get accurate measurements on the amount of material I will need.  The longitudinal stringers will hang under the mast and forward beams.  Then deck beams across will support the planking, which will put the top of it about even with the built-in ledge on the aft side of the forward beam, making it about 3 inches higher than the adjacent decks on the hulls.  The whole assembly will be easily removable as a single unit to aid in disassembly of the boat.