prop pitch

Gday all i have a bit of a conundrum with my boat it is a 6.8m bayshore aluminium hull with a 225hp yammie 4stroke which is currently running a 19 pitch prop i currently get 40knots out of it which i am happy with but i am only getting 4900rpm maximum  should i stay with this configuration or drop to a 17 pitch prop and get more revs out of it and maybe a little bit more top end speed . also would changing the prop and ramping up the revs  make that big of a difference to my fuel economy .

 

Cheers Carry

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sunshine's picture

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Get a wot of 48

Sun, 2015-02-22 19:33

 Same engine on a 6.8 seaqest ......never noticed the revs as at that speed it was bloody frightening, literally skipping across a very flat Sound.    General economy just short of 0.93 litres per NM 

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Date Joined: 18/01/12

there is a couple of things

Sun, 2015-02-22 19:43

there is a couple of things to be noted-

1/ Is this the new F225 or old model?

2/ this fully loaded or lightship?

If that is lightship then it is definitely over propped, if under warranty it could be a problem if there is any sort of failure

Ideally your engine should be propped get close to midway in the allowable range at maximum load, much better that its underpropped lightship than over propped when any sort of load is applied.

Remember that running into a head sea will bog the engine down just as when heavily loaded.

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Carry's picture

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Prop

Sun, 2015-02-22 20:13

gday Rob its the v6 2012 model donk i havent had it fully loaded yet probably only half loaded but didnt seem to make much difference wether half loaded or empty still 40 kn at 4900 rpm also tried playing around with the trim and all the way down it sat on about 4700rpm

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Gday Carry

Sun, 2015-02-22 21:26

 That donk should rev out to mid 5's or more with that prop on that rig. If it were mine I would be having a look at the injectors. 

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forgot to mention-FIRST

Sun, 2015-02-22 21:41

forgot to mention-FIRST before anything else

1/ Has it always done this or only recently?

2/ check/replace all fuel filters in the system, and for kinked fuel lines

3/ Make CERTAIN it is getting full throttle (cable adjustment)!

Wouldnt be the first to go to great expense and find that the problem is more simple

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 Give a man a mask, and he'll show you his true face...

 

 

The older you get the more you realize that no one has a f++king clue what they're doing.

Everyone's just winging it.

 

Carry's picture

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Date Joined: 22/04/09

Revs

Sun, 2015-02-22 22:04

 Gday outwide the motor only has 197 hrs on it but if it is a possibility i will definately get it looked at

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Carry's picture

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Date Joined: 22/04/09

Will check

Sun, 2015-02-22 22:12

 Thanks Rob will check those things out as to wether it has always done it i couldnt tell you i havent had the tub long and i asked the bloke i bought it off and he said he never really noticed i had a mechanic come for a run with me and he seems to think that it is not reving out to what it should so we are going to try the 17pitch prop and see how it goes he also is going to plug the laptop in and check the diagnostics and see what it has actually been pulling. Just thought i would ask and see what a few peoples ideas were.

 

Cheers Carry

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Just saying because

Sun, 2015-02-22 23:05

 the same thing happend to me 18.5 Glass boat could only get 4100 out of it for 31 knots.

Everyone saying thats all folks.

It carries a  F150 Yamaha  after a shit load of rooting around ended up with a service on the injectors. Now wot at 5500rpm for 40knots

JohnF's picture

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Date Joined: 07/07/10

Running too big a prop and

Sun, 2015-02-22 23:06

Running too big a prop and under revving a boat engine is very bad for the engine. IT is NOT like a car engine that responds well with fuel economy and engine life with a low diff ratio.

Unless there is an engine issue, get a smaller prop to allow it to achieve up near redline when lightly loaded and in the middle of the recommended max revs when moderately loaded.

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could well be, Outwide, but

Sun, 2015-02-22 23:24

could well be, Outwide, but ALWAYS start with the simple stuff to save a shipload of money.

These things need to be done methodically

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 Give a man a mask, and he'll show you his true face...

 

 

The older you get the more you realize that no one has a f++king clue what they're doing.

Everyone's just winging it.

 

Carry's picture

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Date Joined: 22/04/09

Cheers lads

Sun, 2015-02-22 23:34

 Thanks lads bit of food for thought there i didnt think it would be that complicated but theres quite a few variables involved i will definately check the basic things to start with then go from there , appreciate the advice .

 

cheers Carry

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Yes Rob

Mon, 2015-02-23 22:40

 You are on the money there. Start with the simple stuff Carry as it could save you dosh.