prop change for yamaha F70LA for top speed

[sevki]

Hi All

My name is sevki and I am from Turkey. we different brands in Turkey so that is why i give some information about my offshore center console boat which has yamaha 2011 model F70LA four stroke engine. You may see the boat here;


the boat is ;

Lenght:203"

Beam: 86"

Dry Weight: 992 lbs

Weight as Tested: 2100 lbs

My propller is Aliuminium K sreies 13-5/8 x 13 pitch

At 6300 rpm I see 31 mph with this propeller.


I want to change this propeller with stainless stell propeller to reach better top speed. I saw some tests on yamaha site with different propeller as you can see here ;

http://www.yamahaoutboards.com/site...jetport_bss_sdc_nx19_f70la_12-10-09_bay_0.pdf

this boat weight very close to me! They reached 35.5 miles with this 14 pitch propeller

Propeller
Series Painted Stainless Steel Series
Diameter/Pitch 13-1/2 x 14
Yamaha Part # 688-45932-60-98


The other one is a little lighter boat here you can see;
http://www.yamahaoutboards.com/site...bss_sct_160sportfish_f70la_2010-11-30_occ.pdf

This boat reached 41.9 miles with 16 pitch same model ss propeller!

Propeller
Series Painted Stainless Steel Series
Diameter/Pitch 13-1/2 x 16
Yamaha Part # 688-45978-60-98


The bad thing is This propellers are not exist in our country. so I dont have chance to try them and decide which one to buy. So I will have to decide one of them and import from other countries! So I dont want to make a fault because I dont have chance to change it after I buy propeller.

My heart says that go for 16 pitch maybe I will see 6300 rpm and will reach the best top speed but my mind says that dont go crazy buy 14 pitch! maybe your your rpm will down too much at 16 and when 5 people get in the ship my boat will be compeletely a donkey!

Thinking and forecast is good but experience always better I need your experiences and ideas about this subject.

 

[steelespike]

Re: prop change for yamaha F70LA for top speed

First a couple of things. The rule of thumb is a 1" increase in pitch will lower rpm "about" 200.
Decrease in pitch will increase rpm "about" 200 rpm.Increase in pitch will slow hole shot,lower rpm and decrease power for heavier loads. I think you can see that a 16" prop will lower your rpm by "about" 600.And will make your boat a "Donkey".
To really tell what your boat can do you need to look for tests of your boat.
What is the brand and model?
I have a feeling your hull is designed to perform well in off shore like conditions. Thus it will be slower than a similar boat
with a faster design but poorer performance in those conditions.
If you go to a ss prop you should start with about the same size prop probably about 1" change 'if any'.
Overall performance "should" be better but don't expect miracles.Your present slip is a very good 6%
Typical slip is 8 to 12% depending on the hull size, design and weight.
A gps is best for accurate speed.

 

[limitout]

Re: prop change for yamaha F70LA for top speed

your outboards safe operating range is 5300-6300 RPM so since you are right at the very top of the safe rpm range you do need a bigger prop then the 13 pitch you have now but the 16 pitch might be too much I think.

others here know more then me but I don't think just changing to 1 pitch higher is going to make much difference in your speed for the expense or replacing the prop so I suggest you go with a 15 pitch prop for it and that should make a noticeable improvement while keeping your (wot) rpms at 5900-6000.

if Yamaha doesn't have one then im sure you can get an aftermarket prop for it. there must be places you can get them where you live or at least a way to get them online.

look here: 15” Pitch Yamaha Outboard Boat Propellers 70 HP 2010 & Newer F70, 4-Stroke - iboats

 

[steelespike]

Re: prop change for yamaha F70LA for top speed

I probably was a little bit conservative thinking of trying to maintain overall performance.
Also hoping he finds some performance numbers based on "his boat", very likely it comes with a Yamaha.
According to the prop calculator if the motor makes 5900 with a 15" @ 8% slip the speed would be about 33.
But keep in mind it may sacrifice some hole shot and may be sensitive to added weight.
I wonder what the rated hp is?

 

[jestor68]

Re: prop change for yamaha F70LA for top speed

A 17 pitch(13.5 X 17 aluminum) should yield about 37-38 mph at your current slip(8-10%) at about 5900 rpm.

A Yamaha or Solas aluminum prop (Yamaha aluminum props are made by Solas) will provide nearly the same performance as SS at less than half the price.

Your selling dealer should be willing to let you try a prop before you buy.

 

[mpsyamaha]

Re: prop change for yamaha F70LA for top speed

A 17 pitch(13.5 X 17 aluminum) should yield about 37-38 mph at your current slip(8-10%) at about 5900 rpm.

A Yamaha or Solas aluminum prop (Yamaha aluminum props are made by Solas) will provide nearly the same performance as SS at less than half the price.

Your selling dealer should be willing to let you try a prop before you buy.

Im not so sure that little four stroke will push any 17p prop to 5900 rpm on that hull. I would think this guy would be in the market for a 15p prop, particularly when carrying any kind of weight in the boat.

 

[jestor68]

Re: prop change for yamaha F70LA for top speed

Im not so sure that little four stroke will push any 17p prop to 5900 rpm on that hull. I would think this guy would be in the market for a 15p prop, particularly when carrying any kind of weight in the boat.

The Mercury prop selector's Yamaha program indicates that it should.

His calculated weight of 2185 lbs used in the calculator included 700 lbs for passenger/gear and 40 gallons of gas.

What pitch he ends up with will depend on actual on the water testing.

 

[limitout]

Re: prop change for yamaha F70LA for top speed

Hi All

My name is sevki and I am from Turkey. we different brands in Turkey so that is why i give some information about my offshore center console boat which has yamaha 2011 model F70LA four stroke engine.
I want to change this propeller with stainless stell propeller to reach better top speed. I saw some tests on yamaha site with different propeller as you can see here ;

The bad thing is This propellers are not exist in our country. so I dont have chance to try them and decide which one to buy. So I will have to decide one of them and import from other countries! So I dont want to make a fault because I dont have chance to change it after I buy propeller.

My heart says that go for 16 pitch maybe I will see 6300 rpm and will reach the best top speed but my mind says that dont go crazy buy 14 pitch! maybe your your rpm will down too much at 16 and when 5 people get in the ship my boat will be compeletely a donkey!

Thinking and forecast is good but experience always better I need your experiences and ideas about this subject.

the more I read and reread your post I get the feeling you never actually got any "real" numbers by taking the boat out and trying it.

you cant use charts or numbers for other boats and think it applies to you and your boat, it just doesn't work that way.

if you try buying a prop the way you are going about it all wrong and you may as well pick one blindly because that is what you are doing. picking the right prop can only be done through testing it on your boat then keeping or changing it based on the results so take your boat out with the prop that is on it now and a full tank of gas and just you or you and one other person and test it. come back and give us answers to these questions and we can give you accurate advice on what prop you need.

first off, make sure you use a gps to measure your speed. DO NOT TRUST the boats speedometer to be accurate but if it is a newer digital one it might be.

trim your motor and tell us the best top speed at wide open throttle -

number of seconds it takes to go from idle to get on a plane -

give us your boat speed at each rpm level in 500rpm increments -

what speed does it begin to plane -

what speed does it lose its plane -

take some tight turns and tell us if it blows out on you (catches air/ventilates)

show us a picture of your motor in its down and level position so we can confirm the cavitation plate is even with the bottom of the hull and it isn't mounted to high or low

 

[steelespike]

Re: prop change for yamaha F70LA for top speed

Finally found the boat. Blue Sea 5.15 CC It's a 17 footer rated for 90 hp so is somewhat underpowered @ 70 hp.
It appears to have a stepped hull.

 

[sevki]

Re: prop change for yamaha F70LA for top speed

the more I read and reread your post I get the feeling you never actually got any "real" numbers by taking the boat out and trying it.

you cant use charts or numbers for other boats and think it applies to you and your boat, it just doesn't work that way.

if you try buying a prop the way you are going about it all wrong and you may as well pick one blindly because that is what you are doing. picking the right prop can only be done through testing it on your boat then keeping or changing it based on the results so take your boat out with the prop that is on it now and a full tank of gas and just you or you and one other person and test it. come back and give us answers to these questions and we can give you accurate advice on what prop you need.

first off, make sure you use a gps to measure your speed. DO NOT TRUST the boats speedometer to be accurate but if it is a newer digital one it might be.

trim your motor and tell us the best top speed at wide open throttle -

number of seconds it takes to go from idle to get on a plane -

give us your boat speed at each rpm level in 500rpm increments -

what speed does it begin to plane -

what speed does it lose its plane -

take some tight turns and tell us if it blows out on you (catches air/ventilates)

show us a picture of your motor in its down and level position so we can confirm the cavitation plate is even with the bottom of the hull and it isn't mounted to high or low

why do you have feeling like that. I tested boat with my humminbird 998 GPS and wrote here but I didnt look at at each rpm level in 500rpm increments. 31 miles is best top speed at wide open throttle on 6300 rpm. Unfortunately my boat is not on the sea now, I only use it on summers so I dont have chance to tell you now what you told me. Here is the photo of my boat. I dont know if it helps.

 

[sevki]

Re: prop change for yamaha F70LA for top speed

Finally found the boat. Blue Sea 5.15 CC It's a 17 footer rated for 90 hp so is somewhat underpowered @ 70 hp.
It appears to have a stepped hull.

Yes you are right here is the link of that boat and the company;

TEKNE YAT?ILIK | TEKNE VE YAT MALZEMELER

It says 90 HP is maximum HP that you can use on that boat.

 

[steelespike]

Re: prop change for yamaha F70LA for top speed

Testing at 500 rpm increments is a little over kill but sometimes can supply helpful information.
Was that bimini top apparatus on it in your test run?
That would surely cost some speed.
Does the boat have a strong hole shot at 2100 lbs?
How does it do with water sports?
Does it maintain slow cruising speed without falling off or requiring constant throttle adjustments?
Don't assume because it new that everything is set up right.
Be sure the throttle opens all the way.Be sure the anti vent plate(just above the prop) is about even with the bottom of the transom.

 

[limitout]

Re: prop change for yamaha F70LA for top speed

why do you have feeling like that. I tested boat with my humminbird 998 GPS and wrote here but I didnt look at at each rpm level in 500rpm increments. 31 miles is best top speed at wide open throttle on 6300 rpm. Unfortunately my boat is not on the sea now, I only use it on summers so I dont have chance to tell you now what you told me. Here is the photo of my boat. I dont know if it helps.

oh ok, sorry about the misunderstanding.

it just sounded to me like you might have just been going by the numbers listed in the links you provided.

as steelespike mentioned, its not needed in 500 rpm increments so doing it in 1000 rpm increments is fine but I think its always better to have more info then less so I always do it in 500 rpm increments.

when you get a chance give us the rpm numbers and answers to the other questions the next time you go out and those numbers will help us tell you what prop to buy