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Boat speed

shelby

New member
Hello Guys
I have a 17.5 foot


Hello Guys
I have a 17.5 foot aq131a/275 and the prop is 14/19pitch and at wot-4800 i get about 35mph is this normal speed or can i do something to get more speed out of her?
When at wot 4800 the carb throttle plate/downdraft is not wide open so when i open no change in rpm?
Thanks for your help
 
"1) I think you are doing

"1) I think you are doing fine speedwise.

2) If you further open the butterfly once the engine has reached the maximum RPM, you will be burning more fuel for no extra output (unless, of course, you are thinking of injecting nitrous oxide
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"EP, thats about the same spee

"EP, thats about the same speed / RPM I get out of my 19ft at WOT. Is that about all I can expect out of her? I was thinking of messing with the prop to see if I can gain more top speed....but from your previous post it sounds like I may be wasting my time doing that. Just curious...what is the typical GPH burn rate +/- at lets say about 4200 rpms cruise speed?"
 
"Ken, it all depends on factor

"Ken, it all depends on factors like the weight and shape of the boat, size and type of prop, etc. When your engine reaches with a certain propeller the WOT RPM indicated by the manufacturer it tells you that any further increase in prop pitch will only prevent the engine from reaching its rated WOT RPM and no further increase in speed on most cases. As an example, with my previous AQ140A and a 17.5' boat, the boat speed at 4200 RPM with a 15x15 prop was just 21 knots and the fuel consumption about 26 liters per hour (or 6.86 gallons per hour). WOT with that prop was only 4600 RPM. However, I used this particular arrangement for thrust rather than for speed, so that the boat could plane at lower speeds even if I sacrificed top end speed. Your arrangement may be completely different than mine."
 
""Cruise" RPMs should

""Cruise" RPMs should generally be limited to 75 to 80% of WOT... Most engines' life at WOT is measured in 10s of hours...at 75 to 80% of WOT, thousands...
1 gph per 10 shaft HP is a reasonable starting point for an estimate for a 4 stroke gas engine,
raw water cooled slightly less efficient.

Re: Messing with prop... with the above scenario, i.e. 4800 max RPM at slightly less than WOT tells me that you MIGHT get another mph or two out of the boat with a higher pitch prop, (your MAX RPMs will drop) but not likely."
 
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