Yamaha 250 prop/rev range question

[kc]

Recently acquired a new absolute fishing "weapon" with a 250 yammy on the bum. Boat has only done 100 hours. Seems to me it is revving way to high for its performance and subsequently using more fuel than expected. Does not have a fuel flow meter but this is on the radar as I recover from the initial purchase but I think it may be under propped as it really needs to be doing 5300 revs to get up and boogy at about 30 knots where the boat feels comfortable and below about 4600 the boat starts to wallow. I recently sold a 150 etec rigged boat which I know was over-propped a little but this ran with low revs, incredible fuel burn and the engine print out was like a new motor at 880 hours. Any comments from experts or 250 yammy owners?

[Daintreeboy]

Is this the motor you have? It says 5000 to 6000 RPM at WOT (page 47 of document.

http://www.yamaha-motor.com/assets/s...07-16_1395.pdf


Or one of these two? Either way the WOT range is still 5000 to 6000 rpm. What is your current WOT rpm?

http://yamahaoutboards.com/sites/def...26-09-96_2.pdf

http://yamahaoutboards.com/sites/def...26-09-96_1.pdf

[Moonlighter]

Kc, what rpm does it get now at WOT? Is it hitting the rev limiter at WOT?

Generally, the new 4 strokes do need to rev considerably more than the old 2 strokes or even the e-tecs.

The guru on here about Yammy 250s is gofishin. Brendan has done more prop testing on them than anyone. A PM to him if he doesnt see this thread will tell you everything you could want to know. In fact if you do a forum search you wll probbay find one of the threads he wrote about this very issue.

edit: here is one of them:
http://www.ausfish.com.au/vforum/sho...ht=Yamaha+prop

[rocklobster]

What sort of boat is it on and what model motor ?

[gofishin]

That was only the start Grant, I tested so many props I needed a prop therapist ...

All Q's as above; 2 stroke or 4? If the latter, F250A, B or D? What boat? How heavy? And yes, WOT at normal trim?

Cheers
Brendon


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[Spaniard_King]

ASk Humdinger, he's got a 4.2L yammy. I recon hes had more props on it than fishing trips

[kc]

Thanks guys,
will get some more info and post. WOT appears to be 6200 but have been an etec man for quiet a few years and never owned a Yammy so all a bit new. Just seems to really only produce decent grunt through a very narrow band of 5200 to 6000. Boat is a Triumph 235 cc (pic attached). 7.2 meters. Will pull some specs as to weight. Boat is at dealer having a Min Kota and new sounder fitted as well as an engine service but will get existing prop specs in the morning. Seems like Ausfish will deliver again!!

Regards

kc

[kc]

Length Overall	23' 8'' 7.21 m	Dry Weight	3,400 lbs. 1,542 kg
Beam	8' 10'' 2.69 m	Tested Weight	N/A
Draft	16'' 40.64 cm	Fuel Cap	145 gal.
Deadrise/Transom	21 deg. - 24 deg. (variable)	Water Cap	N/A
Max Headroom	open	Bridge Clearance	8' 9'' with T-top

[gofishin]

kc, is your motor cowl 'exactly' the same as in the photo? If so it is a 4 stroke and either an F250A or B. The B's came out here in late 2008, and I think the only difference was 'fly by wire' controls.

If your donk (& boat) was imported, the B's were probably released earlier in the US. Regardless, same gear ratio and 'actual/real' HP too (~240 from memory), as my donk.

For comparison, my boat weighs 1,870kg dry and absolutely nothing in it but safety gear & anchor, chain & rope (so quite a bit heavier), 6.85m hull length & prob same overall, and has 20 deg at the transom.

Lightships she does 40kn, so yours should be quicker by a few knots, and definitely should be no slouch.

A lot of yank boats have the donk set up quite poorly, and most singles are way over propped, however at 6200 yours is certainly not!

When you are next running it, check motor height/placement of AV plate in relation to the water at say 20 - 25 kn & normal trim, and the type/model/size of prop. Also check that it is in good condition, no dings or bits missing.
Cheers
Brendon


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[kc]

Thanks Brendan,

Boat runs at 42 Knots WOT with full load of fuel and water and 2 up so does get up and go. Motor is the "B". I had a lot of trouble setting up a 150 etec on a Trophy 6 meter centre console (US import) and ended up have to put a jacking plate on the transom to get the motor up high enough (and got a stack of advice on Ausfish)so I will check the level when running. I never got the "right" propping on the etec which always fell 800 to 1000 RPM short of specs yet performed spectacularly well in terms of fuel burn, maintenance and "longevity" as a result (I assume) of running at pretty low revs its whole working life (used to cruise 26 knots at 3500 RPM and burn 25 litres per hour and burn oil at about 200 to 1. I virtually never ran "hard" with maybe only 30 minutes in its 880 hours at WOT so figure, even swing an oversized prop, in never strained the engine. I have got so used to a low revving engine I am a bit shocked at how high I am revving this new engine and worry about engine life as a consequence, as well as fuel burn as the sweet spot for the boat feels like about 32 to 34 knots but this is getting up to 5500 RPM.

I have read your long post about the 4 blade solas Vs 3 blade. Talked to dealer already about 4 blade. The new boat has a very deep V and the boats (a very small production run) have a reputation for "laying over" in running and are very trim sensitive. No issue with this as the lateral stability if always a trade off for smooth running in sea and I was after the smooth run and so far the boat is sensational and just need to drive right with trim tabs. Dealer thinks the extra grip is a 4 blade may make the boat more prone to laying over?? Never tried one so don't know but I have spend 50 years messing around in boats. Much appreciate your help.

kc

[gofishin]

...the etec which always fell 800 to 1000 RPM short of specs yet performed spectacularly well in terms of fuel burn, maintenance and "longevity" as a result (I assume) of running at pretty low revs its whole working life ....

....I virtually never ran "hard" with maybe only 30 minutes in its 880 hours at WOT so figure, even swing an oversized prop, in never strained the engine. I have got so used to a low revving engine I am a bit shocked at how high I am revving this new engine and worry about engine life as a consequence, as well as fuel burn as the sweet spot for the boat feels like about 32 to 34 knots but this is getting up to 5500 RPM.

kc, don't adopt this philosophy with a 4 stroke, you will kill it!

Every 4/ should be propped to reach the upper half/end of its rec rev range. Pretty sure you will find this is recommended by all the makers.

Don't have any experience with E-TECS, but I suspect over propping and longevity don't go together with this make either. Under these conditions any donk will be labouring.

Re 4 blades, they don't suit all boats/use situations/or skippers. Should be considered on an 'as needed' basis. When they are needed, they are fantastic.
Cheers
Brendon



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[kc]

Thanks for your invaluable advice. I am off to see the dealer now and to run some diagnostics on the motor to see just what it has done and will then talk props with him. Clearly a little under propped at present running to about 6200 or 6300 WOT and dealer is a Solas agent (which I ran on the etec) so should be able to trial a few options over the coming week or so. I also got a fair bit of advice as to getting the etec up to WOT range but just could get it there and then settled into the "lived experience" of running in the rev range and getting such good performance and engine diagnostics I never saw a need to chase different props. Really appreciate your help and will post progress reports as I work my way through this.

Regards

kc

[gofishin]

SOLAS are also very good to deal with direct, however keeping everything through your dealer should encourage a good relationship.

If they are happy to provide a few props to try, and you want to try a 4 bld, an excellent prop from SOLAS is a 4 x 14 1/4 x 17, & used to be called a 'torque master', but they do change names at times. These are tall props and perform more like an 18. It may be an inch small for your boat, but from memory the diam drops for a 19p.

Being lighter, a smaller diam may be ok on your boat (I.e. 14 1/8 or 14), however when I am heavily loaded performance drops off a lot on my rig with these.

Let me know what current prop is, this will fill a few gaps
Cheers


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[kc]

Am now in contact with the owner of the exact rig in the USA via the Triumph Owners forum and he is recommending a 4 blade 15 1/4 inch with 17 inch pitch. Thoughts?

[gofishin]

Always easier/better if you can find someone with exact same rig who has tried different props. What brand prop was that? SOLAS make 4blds at this diam but 18"p is (was?) their smallest

Can he give you a few rpm vs GPS speed figures to compare with yours?

I found with the yams 2.0 ratio (and also a 1.75 ratio & 300hp yam on a lighter boat), that there was not enough available torque to spin a 15 1/4 diam 4bld up well at cruising speeds. Result was too much slip and boats would wallow around cruise speeds. However, at max rpm, where power comes into play over torque, they went well.

These big diam 4 blds work a lot better on zukes, where the higher gear ratio multiplies torque at the prop (slower prop speed) and allows these bigger diam props to work well.

Take 4bld diam down to 15" and its a different story on my boat.

Your boat is different and is lighter again, so just might be ok.

Remember, just because a donk can swing 'a prop' to max or 6000 RPM, doesn't mean that prop is best for that boat.

What is your current prop? Yam? Black s/steel or polished s/s? If the latter, 'M' series (I hope not) or 'T' series Saltwater 2 ??

If you are looking at all types/makes, try a Merc REV 4 if you can. They are only 14 5/8 diam but the high rake means they have large blades and phenomenal grip. When I know what your current prop is I can say what size to try.


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