Sharpie River Cruiser

I would like to build a plywood shallow draft displacement hull river cruiser 24ft. loa x 4' beam thus utilizing 3-4'x8' plywood sheets for the bottom. I basically want a scaled down Bolger Tennessee. Power will be from an inboard air cooled engine with a simple v belt pulley drive. I have several ranging from 5-20hp. My question concerns propeller protection. I would like to explore the option of running the prop in a simple tunnel although I'm not sure the loss of buoyancy will allow it. My second idea is building a keel with a cage protected prop like those used on some river tugs. I have also seen some box keel designs that may provide protection from bottom strikes. Ideas?

 

I've seen at least one design use hull extensions flanking the tunnel for buoyancy.

 

I have built 2 boats, both were welded aluminum planing hull jet drives. One of them had "flotation pods" welded to the transom to counter the weight of the 4 stroke outboard jet.
In this new design, I want to employ a very simple approach to achieve a reasonably shallow draft. I am not interested in speed anymore, rather the simple enjoyment of the journey. I don't see using any larger than a 6" dia. propeller.Would something as simple as an 8"-10" box tunnel that extended approx. 60" forward with the propeller flush to the bottom stay primed or would it just cavitate considering speeds under 10mph.

 

Research the Atkin designed boat called Rescue Minor. It is a remarkably efficient tunnel hulled boat that is well proven and about the size that you have in mind.

The Rescue Minor that I examined at a TSCA gathering, belonged to now deceased Robb White. You might Google Robb White and sons to get hands on information about tunnel hulls.


If memory serves (it does not always serve), boats of this type have a tunnel that is reflexed. That is to say that the tunnel has a tapered closure in back that lowers itself, aft of the prop, back down to the level of the bottom. R. Whites boat would run nicely in eight inches of water. It has/had a little diesel engine that had been filched from a small Kubota tractor. It was about 20 HP more or less. The boat would run 18- 20 MPH, no sweat.

 

Here is a plan for "Heron" by William Garden. This better illustrates the tunnel design. It humps up over the propeller to provide clean flow. It does have vertical sides and would not be too difficult to build.

 

I understand.

Speed is the enemy of just cruising around if one thinks in terms of miles per dollar.

These two are old designs meant for that kind of use and I kinda like them (I'm not terribly fashionable), at least as a starting point:

http://babel.hathitrust.org/cgi/pt?id=chi.103525791;skin=mobile#page/56/mode/1up

http://babel.hathitrust.org/cgi/pt?id=mdp.39015022693538;skin=mobile#page/389/mode/1up

The second is much prettier, the first offers more headroom and such.

Would probably use a feathering wheel though.

 

Src

You know I have looked at Sternwheelers. I have study plans for Atkin's "Lady Of The Lake." Anyway, I'm kind of stuck on my scaled down Tennessee idea. I'm not in love with the tunnel. I think I am more inclined to go with a keel and shoe under the prop provided there is enough rocker to tuck the prop up out of the way astern. I will have to scale my drawing. A complete steel bolt on unit could be fabricated with a doubler on the inside sealed with Sikaflex which handled the shaft, prop, bearings and stuffer, as well as the rudder all in one neat package.

 

There is one possibility that I've seen in a design that wouldn't compromise buoyancy at the stern and that is a tunnel located midships. The design in question was a houseboat with a barge-like hull but I cannot remember exactly where I saw it. Naturally, I've got no idea what it's efficiency would be like.

 

I think in the case of Tennessee, the prop (and tunnel) could be moved forward to the outboard transom position and cutting out the slopwell area creating 2 sponsons on either side.
With the light weight engine at midship and crew forward buoyancy may cease to be an issue although I am no expert on these things.

 

Lots of NAs hereabouts.

 

With a pulley drive ??? With no shifting clutch ??? What about shaft alignment with belt tension ??? Any plans on some kind of thrust bearing ??? .... Just asking.......perhaps i need to be more educated on such installations before making any comments. Its just some things to think about

 

It seems to me that a small outboard in a well, mounted just ahead of transom would be more efficent as a build. It would allow shallow draft , tilt ability, reverse to stop the boat and back up, and would save a lot of money on installing dry exhaust system, and not to mention heat . . Also allows more room for cabin space midship. And what did you say?????? Huh ??? I couldnt hear you over that loud *** air cooled motor...... Just kiddin.... Lol. You definatly found the right place to ask questions. .... Some well educated members here for sure. I dont have time to talk with them, but i read a lot of very useful information on this site

 

To answer your questions;
-an idler pulley(sheave) to engage/ reverse is also possible (been done on rototillers forever)
-engine is inclined 15 degrees (parallel with shaft)
-lock collar behind pillow block for thrust

 

4' beam on a 24' boat is a bit narrow to my way of thinking.

 

Idaho is 31' x 5'3" beam
Tennessee is 29' 11" x 6' beam
I thought I was in the ballpark but I may be a little narrow. I thought I read somewhere about a 6:1 ratio.