Low Horsepower Crusier

Hi all, new to the forum and this is my first post here. Came across this sight on a Google search about efficient hull design. Thought I would post my ever evolving project. I have a 1971 Cal 21 that the rig had seen better days, and refurbishment was just too $. Became a power boat. First with a 6hp Honda off the transom, then electric power to make use of the many electric only lakes in my area. This I believe is the final configuration. My wife and I plan to cruise the intercoastal from Jax to Daytona this fall when it cools down to below the wifes A/C threshold (Nov-Dec). Thats a 6.5 hp Briggs Intek, married to a rebuilt Scott lower case I found at the dump. The Briggs also drives via a belt a 20amp Denso alternator to keep the house batteries charged. So far after 15+ hrs operation all is well with no necessary repairs. Will make 7+ mph on the GPS but thats pushing hull speed, it is more comfortable at 6-6.5. Turns just over 2000rpm@ 6mph averages 1qt/hr of fuel, less in the 4-5mph range. In the never existing theoritical this yeilds 24mpg or a range of 72 mi on the 3gal tank. The old girl sleeps us comfortably and has all the conviences to cruise, less head and shower of course(need to stop anyway). Am pleased so far, abot the only change I am considering is a move to a prop with less pitch as it idles at 4+ mph making docking a little faster than I like.

 

Folks that want to do this may find a rototiller (6-1 reduction) engine a good source of power.

Thrust bearing will be needed, paddle for reverse , but

CHEAP TO BUILD AND KEEP!!

Nice setup.

If you venture further , to the FL West coast, we have dock space FREE for an overnight , on the Caloosahatchie , just East of the Ortona Lock.

Y'all come have a brew!

FF

 

Thanks for the reply and invite! Time constraints will have us limited to the Jax-Daytona-Jax trip. Would love to visit the Gulf though. How about a little more info on your tiller engine suggestion. Your are talking a horizontal engine I presume?

 

Lowhorsepower,

Everything looks good. Can you give a discription of the steps you went through building it? Is that a outboard shaft with propeller?

 

It was as simple as mounting the lower unit to the bottom of the boat, using the original outboard driveshaft coupled to the engines crankshaft with a Lovejoy coupling, and fabbing a simple shifter. I also added a rudder steered by a wheel(original was tiller steered off the transom) and some protective caging for the lower unit/prop. Of course that is an over simplification of the conversion, but those are the major steps. I wanted the engine boxed for sound issues, and basic protection, and that required careful design of the cooling system which worked out very well. The engine note is pretty quiet. My original thought was to add sound deadening but I think it really not necessary. The engine sits on 6 isolator mounts and is modular. Remove 6 nuts on the isolators, unplug one wiring plug and lift the entire uint out of the boat. The sides of the box are quickly removable for maintence or(hopefully not) repairs. I modded the engine some what, so that it runs a pluse pump for the fuel system and installed a cast iron flywheel for smoothness and good idle. The Denso 20amp alternator is mounted to an extended engine mount bolt under the engine deck and is tensioned automatically by a spring. A very high output brushless computer fan evacuates latent heat from the engine box so well that the inside box temp is generally no more that 10 degrees above ambeient. Cooling air for the engine is taken in the foward facing scoop via a sealed tunnel(coffee can and garage door gasket) so there is no recirculation of heated cooling air or exhaust. I guess thats about the long and short of it. BTW the Intek engine has proven to be pretty tough and reliable(I just retired from the small engine trade and saw many an abused one).

 

Lowhorsepower,

Was a backdraft preventer required for the carbeurator or is that only for inboard mounted engines? Would you say Honda GX series are better than the Intek engines?

Also, do you think it would be just as easy installation with a small japanese diesel like the ones available from surpluscenter?

Why did you get rid of the 6hp Honda and how did it compare with fuel efficiency.

 

My 2 cents
I am in the plant hire business and work all day on small 4 stroke engines.
What you have done is great but these small motors like to operate at 3200 rpm when the fan gives best cooling and you have the best torque curve. This is also its best fuel efficiency for rated power output. I dont know if you could do that, but it would be good. This will also mean that when idling the boat is going slow. From what I have seen alternators run at 6000 rpm usually 2:1

 

Goodwilltoall,---- technically I guess this is not an inboard as it is a partially enclosed deck mounted unit, but who knows- no BDP. I think a Honda GX would be a great engine, I am just more familar with the B&S. Having raced a much modded Intek in the open class in karting, I have seen first hand wht these little motors are capable of. As far as a diesel if you are talking aircooled. I believe noise would be an issue to be delt with. I have an 8hp aircooled Hatz diesel that I would like to use in an open utility type boat. Is a hefty, powerful engine but NOISY. I dont know much about the small diesels showing up lately, maybe they are queiter. I still have the 6hp Honda outboard. Really an excellent unit. Id say the fuel economy was similar. I am using the same boat on the same lake with the same 3gal. fuel tank. I would say as a gestimate they are about the same. The water cooled engine I am sure is slightly more efficient, but due to the configuration with the Intek, it is run at a lower throttle setting, so I feel the consumption is very close. I removed the Honda, because it was a transom mount and after nearly 40yrs the transom I felt was suffering from the weight. Also in planing to use the boat in salt water, the idea of circulating the same through an engine set as well with me as the idea of pouring lacquer thinner in a deep cut.

 

Manie B---nice to hear from a fellow small engine person. When you can find the OEMs torque and Hp curves most industrial engines make their fattest torque around 24-2600 rpm with hp rated at the industry standard of 3600. This of course varies with model type and spec#. This Intek was a lawnmower engine and it goverened rpm was listed @3100, well below what it will really turn. I would like to loose an inch of prop pitch which would get the cruise rpm right into the 2400 fat torque area. This engine is running a horizontal cast iron flywheel, which has more than enough cooling fin area to cool this engine at any rpm. The alternator is a Denso automotive type, removed from a small Kubota 3cyl. diesel on the shelf for another project. These type alternators output at a very low rpm. It is overdriven slighty by my selection of pulleys, but it puts out close to 14v @ an engine speed above 1450. Fuel consumption might be better with a more optimized prop/torque/rpm ratio, but I can assure you it is in anycase a non-issue @ around a quart/hr average. B&S lists their outboard@ 2qts/hr @WOT which I suspect is in the upper 3thous. It is limited to 4000 max. My hull speed limits me to a cruise rpm on the average around 2000. Some time we just putt along around 1550@ 4.5mph looking at stuff. Slow crusing aint for everyone, but once you get used to it, its very relaxing.

 

lowhorsepower, awesome setup. having a couple old scott 10hp lower units here I've considered doing VERY similar. are you making use of the S/A's lower FNR shifting rod in the setup?

maybe a T-3 prop is close? http://www.youngprops.com/motorguide.htm
probably have to bore it to shaft size and notch for shear pin,
might be too little on pitch too.. but theyre only 20 bucks with shipping included.

 

An alternator from a diesel is usually not ignition protected. That makes the installation illegal and unsafe.

 

Thanks! I am using the FNR gearing. I have a shift lever with detents for the respective gears. I actually located the detent points before I final assembled the gear case to make sure there was no excessive preload on the shift fork and dog. I actually have the T-3 prop already. I had to bore it to 1/2". I have never tried it. Probably should give it a shot.

 

As this is not a true inboard the alternator should be fine. The engine is located in an engine house, but the alternator is under and outside in free air. It is also cooled by a high output fan which will allow no possible situation for fume build up, and fire possibility.

 

I see. Looking more carefully at the photos it shows that it is an open well.

 

nice job mate.