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Mercury Bigfoot 60 HP

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edsidm

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"For the first time I took my

"For the first time I took my boat out to a place on the river where there are no speed restrictions and discovered that it wouldn't do more than 3400rpm. The manual says it should do 5500rpm. Otherwise, the engine starts well and runs smoothly. Do I have a problem and is it serious? Normally I use the boat where speed is restricted so haven't previously thought there was anything wrong."
 
"I should add that the engine

"I should add that the engine is a 2004 model, the engine oil is clean, and there are no engine management tell-tales. Can anyone offer advice as to what I should do? I have booked someone to do an in-water service but around where I live the river is restricted to 6mph so it is difficult to demonstrate fault. The guy who is doing my service is not a Mercury specialist and may need some advice to the possible fault which is why I am asking for help."
 
"Ian, Tim is definately asking

"Ian, Tim is definately asking the correct question.

Let me take a guess though - you have this on a pontoon boat?

A 60 bigfoot was meant to push alot of weight at low speed. It's gear ratio is 2.3:1 meaning that the engine doesn't have to work as hard as the (normal) model to push a boat through the water that has the hydrodynamic properties of a rock.

If the prop came with the motor from factory there is a great chance that it is "not" what you need on your rig.

Some boats such as pontoons are almost impossible to prop match ahead of time - you really need a tach onboard to determine correct prop pitch..."
 
"Firstly, many thanks to Tim a

"Firstly, many thanks to Tim and Graham for this advice. It is reassuring to think maybe there is nothing seriously wrong with the engine.

The engine is driving a Galeon Galia 530 which is sold as a small GRP sports cruiser. It will have been chosen by the previous owner so I don't know what discussion took place between him and the supplier when the engine/prop configuration was chosen. I don't know what a pontoon boat is, but I can tell you that the Galia weighs 670 kg without the engine and that the manufacturers recommend an engine in the 50-150 hp range. Although I use it on English rivers/canals where there is mostly a speed limit, I can get it to tidal water within an hour by water and open her up. The boat's log book indicates that the propellor is 13p and the diameter (as measured by me) seems to be about 15 inches.

The only other thing that might be relevant is that the boat hasn't been out of the water for 3 years so there may be a coating of blanket weed on the bottom.

May this configuration have been chosen for fuel economy at the expense of speed? It seems odd that the previous owner didn't just put a smaller engine on if he wanted economy.

Thanks again.

Ian"
 
"Ian, if the boat is rated for

"Ian, if the boat is rated for upto 150 horse normal rule of thumb would say that it should have at least 125 horse motor hangin on the back to avoid disappointment (80% of max horsepower).

While a 60 bigfoot is geared lower and will push it along, it will do it at somewhat of a snails pace. Suffient enough for running canals however...

I would suspect the previous owner took a look at the price of a 100+ horse motor and after the shock wore off decided on the 60 which would have come in at about half the price.

Unfortunately, under-powering a rig always leads to disappointment.

If the dry weight of the boat is 670 kgs or almost 1500 pounds, I would peg the absolute minimum horsepower at about 90 horses and more realistically 135 would allow you to experience what the boat can do....."
 
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