Advice please for new Prop.... Bucanneer / yamaha

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Post Options Post Options   Likes (0) Likes(0)   Quote green guy Quote  Post ReplyReply Direct Link To This Post Posted: 02 Oct 2015 at 12:54pm
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Originally posted by nodamboat nodamboat wrote:

Hi Mitch,
 
180 is what I paid for my Yamaha alloy - so at that price, it was just chuck it on, and I'm happy. Achieved the results I wanted.
I reckon I could still do with a smigin more bite, and a 4 bladded job would be the go. But only realised this after running the one I've just got. No major in my books.
 
Couldn't find a stainless or 4 bladed jobby second hand, but if I could of sourced a stainless for 400, I'ld of jumped on it!
 
Was told - rule of thumb, 2" in pitch difference is 400rpm or so difference at top end. Which was about right for me.
 
Chur
Wicked mate as long as its not loading my motor to much with the 17"
these guys here are the ones with the stainless

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Post Options Post Options   Likes (0) Likes(0)   Quote green guy Quote  Post ReplyReply Direct Link To This Post Posted: 04 Oct 2015 at 4:33pm
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Hey Steps I took some figure today, it was solo though so will do a 2 man run on wen.
2000rpm 6.2knots 3.7lph, 2400rpm 7.2knots 5.1lph, 3000rpm 10knots 7lph, 3700rpm 17 knots 8.6lph, 4000rpm 19knots 9.2lph, 4500rpm 22knots 11.3lph, 5000rpm 25knots 14.7lph, 5500rpm 28knots 18.1lph, 6000rpm 31knonts 22.6lph, 6300rpm 33knots 23.9lph 
94km traveled for 30 litres i was causing at 24 knots today though doesn't seam to change much distance wise if i go 20knots or i go 24 knots


I wil do the same thing two up on wen,Thursday.
Today I had 55lites of gas at a guess 100kg of extra gear on board
What ya reckon
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 05 Oct 2015 at 11:15am
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Crunching numbers it looks like u are pretty well propped GG.
Even if throw in another couple ppl.
If anything u have a little too little slip from around 5000 rpms up.. but that could be due to not fully loaded...which would bring u into good numbers.

U have 6300 as WoT.. does it rev out beyond that?  and not asking to go stupid.. if does will it hit 6500 or 6700?  I think the manufacture top limit is 6300 (???)
So hitting 6300 or assuming little over u can afford to go up in pitch
Grip is 'over good' so no need or more cupping blade area... but maybe a little more rake could improve things slightly

If I was looking to a little fine tuning  and found a similar prop in 16 or 17" pitch could borrow..... definjately not worth buying unless have deep pockets

I assume u cruise around the 4000 to 4500 rpms???  the extra pitch and a little more rake would see u cruising in ideal conditions around the 24/25 knots @ 4500  and maxing out rpms around the 6000 @ 34/ 35 kn

Personally the L/ hr thing.. thats real good for when one is travelling  huge distances for hrs on end... eg trawling for marlin all day or heading way off shore, or ferry that sits on the same speed fixed coarse to establish good/ best economy. But for the ave small craft that heads out into the inner gulf, bit start stop drift, with varing speeds, chop, ferry and gin palace wakes etc... over all trip L/ distance as one does in a car is best indicator.

Same thing for say a tractor that spends all day ploughing a field  and a car doing the shopping.....

GG I think your prop engine etc is damn close if not nailed...it maybe worth while trying the alternatives I suggest above but not worth spending money to do so.

Do not get into the trap  some 'hot rodders' get into... they dial in tune in their engines and run sweet, then start to play with a little here little there TRYING to get the doesnt exist 'bit more' ... when then engine etc has already been setup and dialled in..

I note here.. speed is not everything...I increases my top speed... to where the boat chine walks and a /sn commander with full bimini chine walking as asking for some serious accident to happen.. so I dont do it.. period
So also consider a safe and comfortable cruise speed.....which also tends to make economic boating.

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Post Options Post Options   Likes (0) Likes(0)   Quote green guy Quote  Post ReplyReply Direct Link To This Post Posted: 05 Oct 2015 at 6:10pm
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Legend mate thanks, I will get the figures for two pob, just for a looks.
On average a normal trip would be 90km with the odd longer trip here and there, I have got it to 6400 once but backed off strait away. Did notice yesterday even with the crappy wind that came up for 93km I used the same gas than if I was sitting at 20knkts and most of yesterday was at 4500-4800 23knots. Normal Cruze is 4000-4500, guess it is about 3.1-3.8KM per litre something like that
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 07 Oct 2015 at 9:53am
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I have got it to 6400 once but backed off strait away

my question above is VERY IMPORTANT and critical... all of them are

U have 6300 as WoT.. does it rev out beyond that?  and not asking to go stupid.. if does will it hit 6500 or 6700?

The fact that it does go over and how far without being stupid about it makes a HUGE difference to the pitch, cupping , number blades ... the economy , cruise speeds etc... this changes much of by comments above... SERIOUSLY SO
So please need to know how far over goes....

I used the same gas than if I was sitting at 20knkts and most of yesterday was at 4500-4800 23knots. Normal Cruze is 4000-4500, guess it is about 3.1-3.8KM per litre something like that

When we hit uncomfortable chop our gas consumption drops dramatically, even thu trimmed back....stops cavitation and drops the bow into the wave more...
We dont play hero in chop, like our comfort over bang  bang BS.
on the current prop from around the 4000 rpms down u have a lot of slip... trim back in chop and that will increase dramatically if already high. fuel consumption in most cases will increase rather than decrease, and will get the boat  'slowing ' going into/ up a wave and speed up on the other side... a prop with a lot of grip in these conditions and trimmed right, tends to 'chugg' the boat thru at a far more constant speed and better economy.


And knowing how far over the manufactures recommended max... or mid point of the rpm range makes a heap of difference right thru the range and conditions

"number crunching " results is only as good as the data put in... incorrect or incomplete data at best then results in , at best a broad base guide line for a starting point for the old  try this try that hit in miss type methods.

Which raises another question I should have asked... do u know that the tach is reading accurate....its been measured against a induction type tach
And induction tach is one that has coils that wind or clip over a spark plug HT lead

Do a trade me search and they have little ones there about $25 (from memory) and also have an hr meter built in.. self powered .. feed the little wire up the outboard loom, wind and tape the end around the #1 HT lead, and the meter hangs out around the bait board.
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Post Options Post Options   Likes (0) Likes(0)   Quote green guy Quote  Post ReplyReply Direct Link To This Post Posted: 07 Oct 2015 at 10:27pm
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Don't have a bait bird mate but speed is of the gps, witch is about 1-2knots max difference
6400 once and never been able to do that again, not that I have tried but have Wot a few times to see ware it would go I'll drop ya a pm mate after I run two up on Friday
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 08 Oct 2015 at 8:40am
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Trim up at manufactures recommended.. if u can reach that, then give more throttle... if goes over.. then looking at re propping which will improve the cruise speed at lower rpms....like I said  take it up.. dont go over board 500 rpms .....just need it know within reason how far over... and no need to hold there.
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