prop sizes question

 my 5 meter side console traily (yes chinese) has a 75 hp yamy on the back that will only rev to about 4500rpm , its runing a 13/1/4 x 16 prop , i seem to remember the my old 80 yamy that i had on my 5.3 m stacer would rev to 5200 rpm  , i have two spare props from my 80 yamy 13x17 and 13x 19  what should i do to get the extra rpm , also its a bit of a slug geting on the plane 


Darren253's picture

Posts: 352

Date Joined: 23/07/16

That doesn’t sound right...

Wed, 2018-02-07 19:58

That doesn’t sound right... is it a new motor?

the new Yami 75 has a WOT of 6100rpm and you would want to be within 500rpm of that at full throttle. For every inch less in pitch you go you can expect to increase WOT rpm between 200 & 250rpm. 

Sounds like you are significantly over-propped. Might need a complete rethink of the prop range/sizing.

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yes its new

Wed, 2018-02-07 20:02

 yes its brand new only done 5 hours

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the prop

Wed, 2018-02-07 20:07

 its the prop the boat came with what do you suggest i go to prop size 

 

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Date Joined: 17/07/07

go back to dealer

Wed, 2018-02-07 20:11

last time i bought a new boat the dealer exchanged props a couple of time until i got the right one for the boat

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Date Joined: 03/03/10

thanks keg

Wed, 2018-02-07 20:16

 i hadent thought of that but it would be with gritted teeth if  i went back to the dealer  

Darren253's picture

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I changed props 3times on my

Wed, 2018-02-07 20:19

I changed props 3times on my Merc from the dealer.

gruntre69's picture

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Date Joined: 15/10/16

 These dealers should be held

Thu, 2018-02-08 10:38

 These dealers should be held to account in supplying a boat motor package that is propped correctly with the motor also mounted correctly. I also have this problem but unfortunately I wasn't the purchaser of the repower and Hitech Marine don't want to know about it...

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Anyfishwilldo's picture

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Date Joined: 09/02/14

 The dealer does do it, I've

Thu, 2018-02-08 11:39

 The dealer does do it, I've dealt with them in the past... but I did a sea trial before taking ownership and changed the prop twice for no charge. The dealer would be held accountable if the buyer approaches them, regardless of ill feelings. I was in yelling matches when I got my trail craft off them, but they still set the motor up how I wanted it.

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Right on the money anyfishwilldo

Fri, 2018-02-09 22:55

It really gives me the business when you deal with people and all you are asking for is what you have paid for, ie: I want my motor to be blah blah blah and my boat to be blah blah and that is what I'm paying for.

Not to have some retailer how can't be bothered to make sure everything is A1 before presenting it to the purchaser, no ifs, no buts, no excuses.

According to consumer affairs the retailer is totally responsible for the goods he sells to the customer.

The process to gain what you paid for is basically this, you go back to the retailer and "discuss" the situation and how you see it should be resolved. If the situation is not resolved at this "discussion" you write Email what ever to the retailer pointing out that you have not received what you paid for and the "discussion" has not resolved the situation.
Give them 10 working days to respond if satisfaction is not obtained, go to consumer affairs and show them the efforts you have made to have the situation resolved.

Consumer affairs and the retailer get into each others wax and you do not get involved, no stress no anxiety just relax and let the pros handle it. Easy passé.

Darren253's picture

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Date Joined: 23/07/16

13 5/8 x 13

Wed, 2018-02-07 20:18

13 5/8 x 13 Should put you back into the 5300rpm range.
Check the manual and see what the WOT range is. You will get a ton more torque too for getting onto the plane.

Vinesh87's picture

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 Take back to dealer to

Wed, 2018-02-07 20:48

 Take back to dealer to fix

 

Or call Max Ogrady props. They know there stuff!

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Yep, take back to the dealer to rectify

Thu, 2018-02-08 11:46

A good dealer will do a lot to keep his customers happy knowing that because of his good service he is likely to see the same customer in the future.

Quobbarockhopper's picture

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Date Joined: 28/05/10

so your already going for WOT

Thu, 2018-02-08 13:13

so your already going for WOT on a motor thats not run in yet at 5 hours. thatl last

Darren253's picture

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Date Joined: 23/07/16

Whats the problem? Straight from my manual...

Thu, 2018-02-08 13:30

Engine Break‑in Procedure IMPORTANT: Failure to follow the engine break‑in procedures can result in poor performance throughout the life of the engine and can cause engine damage. Always follow break‑in procedures.

For the first two hours of operation, run the engine at varied throttle settings up to 4500 RPM or at three‑quarter throttle, and at full throttle for approximately one minute every ten minutes.

For the next eight hours of operation, avoid continuous operation at full throttle for more than five minutes at a time

 

Yamaha is similar...

2000rpm max 1st hr

3000rpm max 2nd hr

Next 8hr full rev range not being at WOT for more than 5mins at a time.

Ryan C's picture

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props

Thu, 2018-02-08 14:45

 after much trial and error with my new Barcrusher , i have learnt every inch  increase of pitch means 200 less rpm at full throttle but more top speed (2 knts?) , the formula is a 21 inch pitch moves the boat forward 21 inches  with 1 rotation, i went from a 14inch diameter by 19 inch pitch prop 2 weeks ago on my 140 suzuki that was hitting 6500 rpm and (rev limiter) to a 21 inch pitch (14x 21) and gained 4 knots top speed and dropped 3-400 rpm to  6000-6100 max rpm , you need to be careful that the pitch isnt to large and turn your boat into a slug out of the hole.

 

cheers 

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Date Joined: 03/03/10

so here we go

Thu, 2018-02-08 20:08

 boat dealer i bought my boat from  says prop size is problem of the yamy dealer that supplyed the motor spoke to the suppler of the yamy  and tend to agree with them " we water test our boats before we deliver them to the new owner to make sure they have the best   prop for thier boat, its your dealers problem  " i have bought boats of the yamy dealer before and they are good to deal with

Rob H's picture

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 Did you buy the outboard

Thu, 2018-02-08 20:20

 Did you buy the outboard seperately?
If not, if you paid the dealer for the whole lot it does not matter what the dealer says, you have a contract only with the dealer.

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Ryan C's picture

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Date Joined: 08/07/10

Petermac

Fri, 2018-02-09 14:35

 you need to go to a 14 or 15 inch prop Pete if you need more RPM evety inch less will give you approx 200rpm more 

Marineboy's picture

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Prop

Fri, 2018-02-09 16:12

 going by the calcs that every inch less pitch gives you 200 more rpm if you are currently maxing out at 4500rpm it would mean you need a 10 or 11 inch prop to get you just into acceptable wot, geez that’s a very small prop and would that not suggest the boat is a little underpowered ?

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Rob H's picture

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 Pitch not diameter

Fri, 2018-02-09 22:13

 Pitch not diameter

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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.

 

Marineboy's picture

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Date Joined: 14/03/14

Huh

Sat, 2018-02-10 07:53

 small meaning pitch not dia

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Sounds like there wasnt a

Fri, 2018-02-09 19:03

Sounds like there wasnt a water test prior to deliverery. Not suprised concidering were you bought it. 

 

I know different motor but had a 75 merc 4 stroke on my 5.3 traily and ran a 16" prop to 5500rpm.

Raising motor may pickup afew 100 rpms. 

Kyle Evill's picture

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Date Joined: 21/09/10

 Hey Pete,My mate Daniel runs

Sat, 2018-02-10 00:40

 Hey Pete,

My mate Daniel runs a small marine fab business out of Gnowangerup.. Absolutely bloody top notch full bottle in all things outboards. Best bet to give him a call 0448487822 and he’ll give you the run down of pitch versus diameter