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

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    Posted: 23 Aug 2015 at 12:15pm
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Hi all,
 
I'm after a bit of advice for prop selection, for me new waka.
 
It has a  13 1/4 x  17"K on a Yami 130, and revs to 6000rpm not quite at WOT, and aparts from chucking a 19" on ......
 
Should I look for a:
 
Aluminium Prop to keep the cost down....
 
13 1/4 19" keeping the same diameter
13 x 19" Smaller diameter, which seem to be more available eg. Solas / Dunnrite
19" Propellor services
4 blade  12.5 x 19???? eg solas?
 
Rig is a 2000 Buccanneer 525 Escape with a 130hp V4 SWS Yami: max rev's 5500 - 6000
I'm Looking for an economic Cruising Prop for getting to fishing spots 
(I will keep the 17" for water sports)
 
Current 17K is delivering 40 - 42kph (GPS) @ 4200 rpm cruising
Easily reaches 6000rpm at not quite WOT at roughly 58 -60kph (Didn't look at the speedo too much and didn't rev past 6000rpm)
This is loaded with 2 adults 3 kids, say combined weight 250kgs
 
Wanting to acheive a cruising speed of roughly 50kph @ 4200rpm if possible.
 
Thanks for any advice, or if you have a similar rig and can let me know what you run.
 
Cheers
Mike
 
 
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Post Options Post Options   Likes (0) Likes(0)   Quote Ohsoslow Quote  Post ReplyReply Direct Link To This Post Posted: 24 Aug 2015 at 5:30pm
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Hey mate, going off what you've said, and what you're after, I'd probably be looking towards that 4 blade prop you've suggested, 12.5 x 19", while there are a tonne of variables, generally speaking changing to that 4 blade, should give you better bite and stern lift at cruise, helping with fuel efficiency and performance. Being a 4 blade though, it is more like a 20" 3 blade prop, so will likely drop wot rpm by around 5-600rpm.. Which shouldn't be an issue in your situation.

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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 24 Aug 2015 at 6:00pm
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I tend to go along with post above..
Good to see u have  reasonable expectations " roughly 50kph @ 4200rpm if possible." given the motor rating etc...
What is needed to get a far better idea is with the current prop and boat loaded up for normal cruising.
At approx 500 rpms increments from around 2500 thru to WoT  fully trimed on a calm day  the GPS speed at each increment
between each increment...trim up to just before porposing (max trim the faster u go the more trim u can get) and cover a good 150 / 200 m to allow momentum to settle down.. take the rpms and speed

From these numbers  factors such as slip can be factored in to establish diameter , number blades etc... then pitch can be calculated .. and final speeds for any particular prop

Also  keep an eye on trade me props... u can pick up good stainless  4 blade props that cost $600/ 700 for around $200... props are another thing that just dont move
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Post Options Post Options   Likes (0) Likes(0)   Quote nodamboat Quote  Post ReplyReply Direct Link To This Post Posted: 25 Aug 2015 at 8:57pm
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Cheers chaps!
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Post Options Post Options   Likes (0) Likes(0)   Quote Big -Dave Quote  Post ReplyReply Direct Link To This Post Posted: 25 Aug 2015 at 9:58pm
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Hmm, I would say try a few props if you can.
if you can't get to full revs at full throttle, you are over propped, and that's not a good place to be, especially on a 2 stroke.
while I understand what you are trying to achieve, it may not save you any fuel, as it takes X amount of energy to move your boat at a certain speed., if you slow your revs down, you will need to burn more fuel each firing of each cylinder to produce the same power at those lower revs.
you can't fix an idiot with duct tape, but it does muffle them for a while...
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Post Options Post Options   Likes (0) Likes(0)   Quote nodamboat Quote  Post ReplyReply Direct Link To This Post Posted: 25 Aug 2015 at 10:23pm
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Originally posted by Shrekky Shrekky wrote:

Hmm, I would say try a few props if you can.
if you can't get to full revs at full throttle, you are over propped, and that's not a good place to be, especially on a 2 stroke.
while I understand what you are trying to achieve, it may not save you any fuel, as it takes X amount of energy to move your boat at a certain speed., if you slow your revs down, you will need to burn more fuel each firing of each cylinder to produce the same power at those lower revs.
 
 
Hi Shrekky.
 
I got the opposite at the moment, as I can get to the max rpm (6000rpm), at not quite full throttle.
 
Hitting 50kph at cruising revs would be nice, but of course totally dependant on how the new prop goes -  gettting somewhere between 5500-6000 at WOT, and figureing out cruising speed from there.
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 26 Aug 2015 at 10:03am
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I got the opposite at the moment, as I can get to the max rpm (6000rpm), at not quite full throttle.
The manufacture has a rpm recommended bandwidth.. ideally u need to be mid point.. that is where the peak of the power curve is.. but anywhere in that is fine.
And the boat doesnt go any faster and rpms dont increase any more at full trim

If the boat is powered well.. ie not under powered, u will not be full throttle... ie u can go full throttle, but able to pull back on it without effecting rpms and speed..
That is also good for economy

Generally with same basic design of prop (cupping/ rake/ diameter etc, changing pitch  will change to rpms by around 200 rpms
But if slip (like slip in a car torque converter) is too great or too little.. should be around the 8% to 10% at cruise on a cruise settup, one can then fine tune with props with more blades, more rake more cupping or bigger diameter
This can make huge differences in economy at different rpms... and speed efficiency
One can speed a lot of time, lot of money messing around with different props, or can take 1 or 2 props... take a few numbers as I suggest above.. sit down crunch a few numbers and come up with a prop of a given pitch , diameter , rake cupping and blades that will either be spot on or very close... with numbers off that prop... and borrow one thats close or same as the number crunching indicates....and look at  trademe and or purchasing what YOU NEED for YOUR USE of the boat
Our boat was  'professionally' hit in miss proped by the previous owner
Basically was "an old heavy hull" BS thing
We weighed the boat fully loaded.. old heavy boat BS went out the window.. and confirmed the theoretical weight within 12 kg from number crunching.
From there found slip was 27% at cruise and 12% at wot....thats like driving a car with a very baddly slipping clutch !
Borrowed a slightly better prop (not what wanted).. worked out what the theoretical results would be before hand  and actual results where very close.
Numbers off the original professionally propped prop and the borrowed , after crunching numbers and measuring differences in surface areas....still said need  19 pitch and 14 1/2 to 14 3/4 diameter std prop .. or and after market 14" with more rake and cupping... or around 13 t 13 1/4  4 blade with good rake and cupping

Now keep in mind all have done to date is 2 runs, on 2 props that are known to be wrong
Problem now was they dont make a std prop over 14" diam.. and props with more rake and cup dont make over 13 1/2".. which left a 4 blade option
About this time a 4 blade stellto phase 2  13 3/8x 19 pitch came up on trade me for $150/ 200 (cant rem.. but thats around $700 new)
Drop that on
old cruise at 4200 was around 27 mph  top speed about 40mph and WoT marginal over manufactures recommendation
The theriocal and real result of the new prop,  keep in mind it is not the ideal with diameter 1/4 to 3/8" over size... top speed of  just over 43 mph 700 rmps less than before which was chine walking fully loaded and scarry in a cabin boat with bimini...and cruise at 3800/ 400 around 35 mph  
AND just under a 50% better economy !
Down side...Im marginally under the manufactures min rpms by about 150 rpms.. not serious but also not good IF I decide to be stupid and chine walk the boat..
At cruise there is still a satisfactory margin between the hp requirement of the prop to the power out put of the engine at the prop at that rpms.. so engine is not loaded.

Now in say all this, several experience members here have been out with us, and can confirm different parts of the above, and one has been out during the changing of props etc ...

Numbers work and work better than hit in miss experiments , cheaper and far less messing around.

So for now Im just looking quietly on trade me for a prop same as currently use  lightly smaller diameter to give slightly more slip at WoT to put WoT rpms back in the manufactures spec  in theory give marginal more top speed that dont need, loose a mph or so at cruise .. still over the 32 mph, and theroeally gain 2 or 3% improvement in economy.

So if u want to post up those numbers fully loaded, some time, your gear box ratio....prop (s) specs I will crunch up for u or u may like to read thru this stuff
http://continuouswave.com/whaler/reference/propellerPowerCurve.html
http://continuouswave.com/cgi-bin/crouchcalc.pl


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Post Options Post Options   Likes (0) Likes(0)   Quote nodamboat Quote  Post ReplyReply Direct Link To This Post Posted: 29 Sep 2015 at 10:52pm
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Hi Keith. (Steps) Good to bump into you at the ramp today.

With the elcheapo YYamaha 13 x 19 prop today. Boat went well.

Only lightly loaded but picked up good 8 or 9 kph at cruise now just over 50kph and top speed a bit over 70.

Need to look at the trip numbers from the gps and top the tank up next time I go out and figure out exactly how she's doing.

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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 30 Sep 2015 at 9:03am
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Was that u out around the bay on Pakatoa killing time with a few drifts till the tide was far enough in to load boats at the ramp?
How did u do? 
Again this winter has been the hardest fishing in recent yrs... we brought back a couple nice feeds but not enough to fire up the smoker today.
Even the long line on got a couple underside.
But a nice day to be out on the water with the family.
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Post Options Post Options   Likes (0) Likes(0)   Quote nodamboat Quote  Post ReplyReply Direct Link To This Post Posted: 30 Sep 2015 at 4:03pm
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Was hard work alright, managed 5 snaps and 1 kahawai. 1 snap big enough for a smoke, but was out all day - was a bit hard work.

All males and they all had empty tummies.

Was at Pakatoa briefly, but only dragging for a couple of scallops in the arvo.

Yeah turned into a mint day. Kids will be keen to get out when they get back from hols.

Cheers Mike
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 30 Sep 2015 at 5:29pm
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That was us down the other end.. then inside the reef sth end...heaps of sting ray collected there
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Post Options Post Options   Likes (0) Likes(0)   Quote green guy Quote  Post ReplyReply Direct Link To This Post Posted: 30 Sep 2015 at 10:03pm
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hmmm this number crunching sounds hard but I'm going threw the process as well i want a higher speed cruze i am still getting 6200-6300 with 2 people and gear so think I'm a lil under proper may be i hit 6300 rpm one on board to any way think I'm gonna go stainless with a 16" it can be a painful process all right and expensive one too
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Ideally one chooses the boat.. then crunches the numbers to establish what HP is required to meet the expections of cruise speed, economy and WoT
But if already powered...
Need to know several things
1/ fully loaded weight of the boat.. and type of hull
2/ Engine HP rating.. gear box ratio...manufactures WoT rpm range
3/ what the boat to be used for most of the time ...eg  cruise to fishing spots at reasonable speed and economy.. or all out race boat..or pulling up skiers/ towing or primarily use to troll.
Comprose of any of these results in compromise across the board.
Personally if general fishing , checking out the gulf .. good economical cruise speed.

But any of the above  to reach expectations means correct power theoretical  power plus 15 to 20%

Since u already are powered.
Your expectations of cruise speed at what rpms.. and top speed.. WoT
Gross weight of boat
Hull design
Engine HP gear box ratio
The current prop spec.. Diameter Pitch stainless or Ally, number blades and if possible manufacturer

And on a calm day.. fully loaded up starting around 2500 rpms in approx 500 rpm intervals thru to WOT.... the GPS speed
At each stage.. fully trimmed to just on the point of porpoising.. travel a couple 100 meters and take your reading.. the repeat next stage re trim etc.

From there we can do some crunching.

From memory u have a sea nymph 14' 6" ?????
Very general ball park powering 4m 50 hp  5m just over 100hp 6m just under 200 hp...
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Here, crunch some numbers.
A spreadsheet I put together. Should be pretty self explanatory 
The 4 R's ~ Rods, Reels, Rifles, Rooting
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Post Options Post Options   Likes (0) Likes(0)   Quote green guy Quote  Post ReplyReply Direct Link To This Post Posted: 01 Oct 2015 at 9:42pm
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Yip 14.6 sea nymph, Yamaha 2016 F70 four stroke, 2.33:1 ratio gear box, 13 1/4 15" alloy prop.
I have no idea of the boat weight, loaded with one but i would say 450ish.
I am going to do some test on sunday and will get back to you steps but i am hitting max RPM with one or two on board 6300RPM just speed is affected, 33knots on a good day or 30-31 knots 2 up.

cruze at 4100 RPM one up at 20 knots, 2 up is more like 4300-4400rpm
on the plane at same speed 3300rpm depending on the sea but flat is the same result.

My goal is for a lil high speed for cruzing, not fussed on top end.
Had a chat to family boats today, they are suggesting a 17" alloy prop, i should get no less than 5900rpm two up with all the gear etc other wise it may be to much pitch
$180 for a alloy prop $800 for stainless.
Thinking of biting the bullet and going with the 17" alloy 
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Originally posted by green guy green guy wrote:

$180 for a alloy prop $800 for stainless.
Thinking of biting the bullet and going with the 17" alloy 
Good price for alloy prop.  If you can crunch numbers and be confident in them (or borrow another prop to test) and intend to keep the boat for a few years - go Stainless!  Lot more durable and better performance.  Steps mentioned keeping an eye out on trade me and buying second hand when suitable turns up?   I bit the bullet and bought my stainless prop 300hrs ago and still mint - alloy props don't last IMO and would have needed repairs by now.
Good fishing trip nothing breaks, great trip catch fish.
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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 7:17am
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Can get a stainless for $400 but would rather try befor i bite the bullet
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Will Family Boats lend you an alloy prop, Mitch? 
Semper in excreta sumus, solum profundum variat....



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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 11:29am
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Na mate i asked yesterday 
i will try the guy's at Trev Terry marine ware i got the engine, guess its one of those things
They are in Tauranga though so am not expecting them to help out. Think ill bite the bullet and just buy a alloy prop and go from there not much els i can do really
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Post Options Post Options   Likes (0) Likes(0)   Quote nodamboat Quote  Post ReplyReply Direct Link To This Post Posted: 02 Oct 2015 at 12:04pm
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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
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