Jim Michalak's Boat Designs
118 E Randall, Lebanon, IL 62254
A page of boat designs and essays.
(1jan01) This issue shows how I made a tiller extension for my old outboards. Next issue, 15jan01, will discuss mast tabernacles.
Joe Millard in his lug rigged Tween.
Outboard Tiller Extension
...You might recall from last issue that my AF4, loaded heavily with two men and two motors, sped up as Max walked forward in the cabin slot as we were testing with an old aircooled 5hp outboard. I got my copy of Hullforms6s out and checked the trim of the boat after figuring out some weight and cg combinations. Here is how Hullforms trims the AF4 with a total weight of 850 pounds, two motors on the transom, one man at the motor tiller, and another man in the forward part of the cockpit. When you look at these the important thing to see is where the waterline crosses the hull bottom in the front, and again where it crosses the transom.
Hullforms predicts that the draft at the stern is 4.6" in this condition, with a waterline length of 12.6'. Then as Max walked forward into the cabin slot 4' the cg moves forward about 13". Hullforms shows the boat trims down about a degree, reducing the draft at the stern to 3.5" and lengthening the waterline to 14.1'. Then it looks like this:
I think both factors resulted in an increase in the speed. But we didn't measure the difference in speed although we could feel it, see it in the reduced wake, and hear it as the motor sped up.
Later I went back by myself with just the 5 hp motor, a total weight of about 560 pounds. With me back at the motor tiller the boat went 7.2 mph. Hullforms predicts the following trim, with 2.6" draft at the stern and a waterline of 12.2':
Next I ran the same course but with a 4' long tiller extension, so everything was the same as before except that my weight was forward. The boat sped up to 7.8 mph. Hullforms predicts the following trim:
The waterline extends to 13.7' and the maximum draft is still 2.6" but it is not at the stern.
So performance is increased with the same motor as the skippers weight moves forward. I'm not certain if this would happen if the boat were planing. That might be a good test for next year. Also it would be interesting to run the weight forward until the stern is totally clear of the water. (At one point Max walked all the way forward in the cabin slot, the boat sped up more but the steering was getting spooky.)
There are other good reasons for the tiller extension even if performance does not increase:
.....Visability over the cabin is improved quite a bit when you can sit at the cabin bulkhead instead of back with the motor.
.....Motor noise is greatly reduced, at least to the skipper's ears. If he sits say 6' from the motor instead of 2' then noise the might be one ninth. This is noticable even with a short tiller extension. Also vibration at your steering hand is reduced.
.....Directional control can be improved because tiller adjustments can be a lot finer. True even of sailboats and Bolger has said that one way of speeding up any sailboat is to lengthen the tiller.
MAKING THE EXTENSION...
... was quite easy for motors like the Sears 5. They do not have a twist grip throttle. All I did was find a length of very light wall aluminum tubing that slipped right over the tiller. That was easy! It must slip off easily too since when in tight quarters you will have to remove it and handle the tiller and its sliding throttle directly.
My Sears 7.5 and my Johnson 10 have twist grips. And neither has a tiller grip that is constant in diameter.
I bought a length of schedule 40 PVC pipe, 1.5" diameter. It would not fit over either handle. I cut a section 2' long. I cut four slits in one end, 5" long which would pretty well cover the tiller grip. I drilled a small hole at the end of each slit to hopefully stop any cracking at the end of the slits. Now to form the PVC pipe over the twist grip.
Now the real fun begins. I had found that PVC can be heated to a consistancy of rubber by playing it near my kerosene powered shop Rediheater. I'm not too sure what other heating methods might work - an ordinary stove top might do the job too. But with the shop heater I put the slotted end of the PVC about 6" from the heater's flame delfector, twisting it to get even heating all around. Wear gloves. I think it takes a minute or so to get to the rubber stage, but check the pipe every few seconds until it is ready.
Once rubbery, the PVC will stay that way for a minute or two, long enough to push it over the end of the twist grip, and to reform it down onto the grip with your gloved hand. Let it cool there. It will return to its rigid state, but you probably will be able to spring that slotted end enough to get it on and off now at will. Here is what a new one looks like on an old Johnson. (If you think the photos were taken in a cave I will mention that we are in one of the worst winters in memory right now.) You can see the slits and a bulge where the heated pipe expanded over the end of the tiller handle:
Push it back on and clamp it down with a hose clamp. You are done! It will be quite solid. The large diameter pipe I find to be very comfortable. Here is another clamped in place on a Sears 7.5:
AN EXTENSION FOR THE EXTENSION...
... One day I went out in AF4 with the Sears 7.5 and the above tiller extension. I also had on board the 4' long extension for the smaller motors which have no twist grip throttle. I slid the long extension into the 1.5" ID extension on the Sears and found the twist grip had enough friction that it would stay set at part throttle for long enough for me to move my chair forward near the cabin bulkhead and steer with the long extension. Quieter, less vibration on the tiller hand, and better vision over the bow, but the motor always would vibrate the throttle setting down and every few minutes I had to reset it.
I bought a section of 3/4" ID PVC pipe and cut off a piece 4' long. It fit fairly loosely into the larger pipe. I "padded" it to fit snugly, but still loose enough to allow it to be removed quickly. First I slid the small extension into the larger as far as it would go and marked where the pads should go. To make the pads I took two 1" sections of the smaller pipe and cut them into four segments of 90 degree arcs. I fit them to the inner extension by sanding with very coarse sand paper. I glued them to the inner extension pipe as shown below:
After the glue cured I sanded the outside of the pads until I had a slip fit into the large tiller extension.
It had no slop now and the final step to the twist grip throttle was easy. I pushed the inner extension inside the outer and drilled a 3/16" hole through all of them about 5/8" from the end of the outer extension, right through the pad that was there on the inner extension. I removed the inner extension and installed a 3/16" pin through the hole with length long enough on each side to engage the matching hole in the outer extension. Then I cut the outer extension so that the holes there became slots. Now to install the long inner extension, it is just a matter of pushing it in place until the pin engages the slots. Twist away!
Here is what it looks like on the Sears 7.5:
I can operate the motor from the aft end of the cockpit, when in close quarters when I need to operate the shift lever, with the inner extension removed. Once in more open water I can slide the long extension into the tiller and sit or stand right up by the cabin bulkhead.
The entire rig cost maybe $10. It is a lot cheaper and simpler than remote controls, especially since I switch motors so often.
Will present some thoughts on mast tabernacles.
CAMPJON, CUDDY JONBOAT, 15.5' X 5', 300 POUNDS EMPTY
Campjon is based on my Jonsboat design. I increased the hull depth to 24" from 18" and again to 30" in the region of the 6' long cuddy cabin. The cabin decks slope upward towards the center so the "headroom" in the middle is about 3', usually that is enough to allow sitting up while seated on the floor. There is a slotted walkway on the cabin centerline just like I've used on my AF sharpies, but this one also has a step through to the front deck. The front deck itself is fairly large and easier to use as a boarding platform than with the AF sharpies. But it is very important to NEVER let anyone ride on a front deck like this when the boat is in motion. If they slip off the deck they have no option but to slide under the boat full length and through the prop in an instant.
I doubt if the increased freeboard makes the boat any safer since a flat boat like this is not good in rough water in any case. The higher sides do give a feeling of greater security since this will be a boat you are "in" instead of "on". This would be a better family boat since the kids can be kept cornered in the cuddy while underway. They can stand in the slot, or look out the front or out the windows. I suspect the cuddy will find a lot more use as a spot for the portapotti than as a camping cabin. The cockpit as drawn has no seats and is itself a big playpen. For seating I suggest using common folding chairs like I have used with satisfaction on my AF4. When the boat is not underway the chairs are folded and stowed, or relocated to another part of the boat or the shore.
As for power I would suggest a good 10 hp motor to keep the capability of using the smaller lakes which are wisely limited to 10 hp. With two normal sized adults the boat should plane, and be very lively with one aboard. I should add that the Coast Guard has suggestions about powering small boats and they come down hard on flat bottomed hard chine boats like jonboats because of handling concerns. I think they would advise a max of 25 hp in a hull like this. I would advise a max of 15 hp. (My AF4, which is about the same weight as Campjon, went 22mph with a 40 year old Johnson 18.) There is a draining motor well in the stern.
Constuction is nail and glue, with no jigs or lofting. From four sheets of 1/4" plywood, two sheets of 3/8" plywood, and two sheets of 1/2" plywood.
Plans for Campjon are $20 until one is built and tested.
Some of you may know that in addition to the one buck catalog which now contains 20 "done" boats, I offer another catalog of 20 unbuilt prototypes. The buck catalog has on its last page a list and brief description of the boats currently in the Catalog of Prototypes. That catalog also contains some articles that I wrote for Messing About In Boats and Boatbuilder magazines. The Catalog of Prototypes costs $3. The both together amount to 50 pages for $4, an offer you may have seen in Woodenboat ads. Payment must be in US funds. The banks here won't accept anything else. (I've got a little stash of foreign currency that I can admire but not spend.) I'm way too small for credit cards.
Here are the prototypes abuilding that I know of:
Caprice: A brave and experienced builder in Texas is making the 25' Caprice water ballasted sailboat. A big project that looks bigger with each new photo.
Jon Jr has been completed by Joe Leinweber and Dan Ellis and tested to a certain degree. Click here to read about the test and the surprize ending! ("The waters are only safe until next time!")
Skat: I'm told the prototype Skat project is underway again and very close to being done.
AN INDEX OF PAST ISSUES
BACK ISSUES LISTED BY DATE
Mother of All Boat Links
Messing About In Boats
The Boatbuilding Community
Kilburn's Power Skiff
Bruce Builds Roar
Rich builds AF2
Herb builds AF3 (archived copy)
JB Builds Sportdory
Hullforms Download (archived copy)
Plyboats Demo Download (archived copy)
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