External Combustion
Chief Petty Officer
- Joined
- Aug 21, 2007
- Messages
- 608
OK outboard guys! Here is the stumper. I have read here that outboard engines should not be ran at low to medium R.P.M.s as they coke badly, pull ring lands and otherwise have bad juju unless they are ran near w.o.t.
High RPMs with high prop slip is excessively bad on economy and leads to high engine wear, so.... for those of us who are displacement boat fans (1.34 times the square root of the waterline length equals slow and slower) what are the outboard options?
I have seen several heavy river cruisers (20K to 30K pound class) that were outboard powered. Two of them had to have twenty year old engines on them.
My own personal outboard experience does not involve much slow speed work, yet I have had no coking problem or lube defficiencies in several thousand hours of just putting around. I know that there are lucky fools and I may well be one.
That is the reason I am asking. What would you recommend for producing just enough HP to the water to push a displacement boat to it's natural hull speed? It usually involves 4 to 6 internal combustion HP per ton of displacement.
The flat bottomed cruisers that I am looking at will go semi-planing speeds, which is important when trying to go upstream on the lower Mississippi or other rivers that have 4 to 6 mph currents, so a comfortable excess of power is welcome. We displacment guys just don't want to feed all the horses in the stable if we are only going to use them a few times a year. We would rather travel ten miles on a dollar as compared to one.
High RPMs with high prop slip is excessively bad on economy and leads to high engine wear, so.... for those of us who are displacement boat fans (1.34 times the square root of the waterline length equals slow and slower) what are the outboard options?
I have seen several heavy river cruisers (20K to 30K pound class) that were outboard powered. Two of them had to have twenty year old engines on them.
My own personal outboard experience does not involve much slow speed work, yet I have had no coking problem or lube defficiencies in several thousand hours of just putting around. I know that there are lucky fools and I may well be one.
That is the reason I am asking. What would you recommend for producing just enough HP to the water to push a displacement boat to it's natural hull speed? It usually involves 4 to 6 internal combustion HP per ton of displacement.
The flat bottomed cruisers that I am looking at will go semi-planing speeds, which is important when trying to go upstream on the lower Mississippi or other rivers that have 4 to 6 mph currents, so a comfortable excess of power is welcome. We displacment guys just don't want to feed all the horses in the stable if we are only going to use them a few times a year. We would rather travel ten miles on a dollar as compared to one.
