Speed Question

jcwads

jcwads

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Hi All

I have a single D4 260. It can prob do 35 knots plus.

When out today in a pretty windy sea state the boat maxed out at 27 knots full throttle. I had had the boat at 32 knots easily earlier in the day!

I looked at the instruments and the engine heat dial was on over 200 just on the red.

Slowed down and it went back to a steady 180 degrees.

Anyone know why the speed may have been so restricted? Is this normal?
 
The sea state can disrupt the boat's speed, which puts more load on the props as the engine will try to get the boat back to its maximum speed. WOT and max engine speed are closely inter-related. If the boat slows then the prop effectively has to push more water past, increasing prop load and engine load, but as revs drop the power the engine is developing also drops, so it will start to labour, causing it to overheat.

The WOT, max revs and engine load will likely vary according to the direction of travel relative to the sea's motion, and if the engine can't achieve WOT max revs than you should back off to avoid overloading.

There is also the possibility that a more violent motion could stir up crud in the tanks which could be causing the filters to block and hence restricting the fuel flow to the engine.
 
Rise in exhaust gas temp due to overloading .
Cumulative wear and distortion of the valves particulary the exhaust valve seat ,loss of power /torque .
You ran it too long in an overloaded state ,trying to max it .
As small overheat of 200 not too bad ,but neither is it doing it any favours ,the rings expand , oil thins out and possibly a ring cracks = loss of power compression -- try a blowby test ,next time you go out at a "reasonable " rpm remove the oil filler cap .if there's a lot of pressure ,your rings or valve guides are shagged .

Fouled hull and or props ,most likely props lead to the temptation to overload it .
Cos the broschure said X knots @Y rpm .
 
Gps sog only works to erasure boat speed through the water if you allow for tidal flows assuming you are on the sea if you do consecutive runs over the same stretch of water back to back and average the speed. These runs need to be with and against the current not across a tidal flow as well.

Say where you did your two runs at 32 and 27 knots there was a 2.5 knot time running one way would over read by 2.5 knots the other underread by 2.5 knots.

A log gives you speed through the water.
 
Any buzzers sounding ?
These engines have a gaurdian mode which restricts power under certain conditions.
 
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