Camanos 31 Owner's Handbook Manual - page 10
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run the engine up to full throttle and then read the tachometer to determine the maximum RPM. If you
are carrying a full load of fuel and water plus enough spare parts to build another boat, your engine's
RPM will be considerably lower than if you were running light. Similarly, if you allow more and more
marine growth on the boat's bottom and prop, your maximum RPM will gradually decrease.
Maximum RPM
According to the manufacturer, your Volvo diesel engine can be operated at 10% (approximately 400
RPM) below maximum with no detrimental effect. You mus t take care, however, because this is where
you can run into trouble. This engine is rated for a maximum of 3900 RPM, which you should always
be able to achieve in a fully loaded condition and with a clean hull bottom. If you find your engine's
maximum RPM to be 3900 at the beginning of the season and run the engine for the rest of the year at
3500 RPM, it is likely that at some point, because of increased bottom growth, your maximum RPM
has dropped to something lower than 3900 and you will be over working your engine without realizing
it. To avoid this, check out your boat's top RPM once a month and stay a minimum of 400 RPM below
it in order to be safe. Remember that this is your absolute upper cruising speed and a limitation that
you should not go beyond. Anything below that should be considered your actual cruising speed.
Useful Tip: If the maximum RPM decreases by 150 RPM or more during the course of a season then it
is likely because of (1) a foul bottom, (2) added weight, and, less likely, (3) incomplete combustion
(black smoke) or (4) restricted air intake (black smoke).
It is also worth keeping in mind that as the weight and/or the drag of the boat increases the more
performance is negatively affected and the more fuel you will burn regardless of cruising speed.
Similarly, regardless of the weight or drag, the higher the cruising speed of your boat, the more fuel it
will consume per mile. Obviously, since most things in boating are a compromise, you will have to
juggle the three variables (weight, drag and cruising speed) to accomplish your goals.
Given the foregoing, a significant increase in range is easily achieved by making long passages at slow
speed. Keep in mind that high speed and long range are mutually exclusive -- if you have one, you
can' t have the other. If you wanted to increase your range while running on plane, you would have to
increase your fuel load, the weight of which would reduce your speed and increase your fuel
consumption. Obviously, any attempt to combine high speed and long range will quickly reach a point
of rapidly diminishing returns.
If more range is required for the few long runs you wish to make, you are better off to add temporary
fuel storage rather than add more permanent capacity. Which brings up another point. If you are not at
dock and in the middle of a petroleum- free zone, how do you transfer your extra fuel into the fuel
tanks? If you try to fill them from the aft deck with a five-gallon Jerry can, you will have the pleasure
of knowing what happens when you pour oil on troubled waters. Instead, use a long hose, fitted with a
funnel that will reach from the bridge deck into the fuel tank deck plate openings.
Useful Tip: There is an area in the engine room above the prop shaft and against the aft bulkhead to
secure extra fuel by inserting a plywood shelf. Be sure the fuel is well restrained.