Props explained please.. - Page 2

chewy · 11 September 2009, 20:07

Quote:

Originally Posted by JSP

Jesus! £££

££££

You also have prop slip, you need a little bit but not too much.

Chris · 11 September 2009, 21:12

Quote:

Originally Posted by JSP

When turning tight, the prop can slip very easily. Also can loose grip when things get lumpy

Losing grip is probably going to be down to the following

- Engine is trimmed out (most will slip when running trimmed out when you turn tight)
- Prop is damaged (even small nicks and dents will cause cavitation and the prop will loose grip more easily)
- Engine too high on the transom

Post a pic of your prop so we can see what condition it is in....

doggypaddle · 11 September 2009, 21:20

yamaha K series 19 or 21 will be about spot on i would say.
Most yam90s on seariders run 19" props, you should be able to swing a 21 with the extra power of the 115.
NOS4r2 has a 21 on his SR at the moment cos the hub on his 19 went.
thats OK with an 85 rpm wise (just) should be dangerous fast with the 115

Perhaps if there time at the gathering and you can persuade NOS you can try the 21, he can use my 19, and i will run on a 17" i have?

JSP · 11 September 2009, 22:04

Quote:

Originally Posted by Chris

Losing grip is probably going to be down to the following

- Engine is trimmed out (most will slip when running trimmed out when you turn tight)
- Prop is damaged (even small nicks and dents will cause cavitation and the prop will loose grip more easily)
- Engine too high on the transom

Post a pic of your prop so we can see what condition it is in....

Thanks Chris,
I always trim in to do the turn. True it could be trimmed out a bit to far when I've lost grip in the waves.
Prop is fine, no dings.
Didn't think about the engine...Will take some pics as soon as

JSP · 11 September 2009, 22:06

Quote:

Originally Posted by doggypaddle

yamaha K series 19 or 21 will be about spot on i would say.
Most yam90s on seariders run 19" props, you should be able to swing a 21 with the extra power of the 115.
NOS4r2 has a 21 on his SR at the moment cos the hub on his 19 went.
thats OK with an 85 rpm wise (just) should be dangerous fast with the 115

Perhaps if there time at the gathering and you can persuade NOS you can try the 21, he can use my 19, and i will run on a 17" i have?

Bugger, my boats not coming to the gathering mate. Thanks though

I've seen a few new 21" K series for sale. Wonder if I should just take the plunge?

chewy · 11 September 2009, 22:11

Quote:

Originally Posted by JSP

Bugger, my boats not coming to the gathering mate. Thanks though

I've seen a few new 21" K series for sale. Wonder if I should just take the plunge?

How come your mot bringing the boat mate, trouble with console?

JSP · 11 September 2009, 22:13

Quote:

Originally Posted by chewy

How come your mot bringing the boat mate, trouble with console?

No and yes, Consoles glassed in but I've got my lads birthday party tomorrow, my girls on Sunday then their actual birthdays on Tuesday and Wednesday and bugger all time inbetween then and the gathering to finish it all off

But I may not be seariderless that weekend

Hightower · 12 September 2009, 11:14

Once you've sorted the slip out buy adjusting the trim or engine height out the next figure I would be looking at is my cruising speed at a set RPM (say 3500rpm) and seeing what speeds I'm getting with different props.

It's all very well looking for the holy grail and getting maximum speed, but max speed doesn't always mean max speed at cruising RPM

If you could eek out another few knotts at you're normal cruising speed then think of the fuel savings and decreased travel time.

Nos4r2 · 12 September 2009, 11:37

Quote:

Originally Posted by Hightower

If you could eek out another few knotts at you're normal cruising speed (assume you mean RPM) then think of the fuel savings and decreased travel time.

Erm, but that's making your engine labour.

Let me put it this way.
Basic principles:-

Your engine develops it's rated HP between the max rpm figures stated by the manufacturers.
If you can't rev to the rated RPM, you're not developing the stated HP and you're using more fuel per combustion cycle (but less cycles) to keep the same performance, yet losing acceleration and not doing your engine a whole lot of good.

Hightower · 12 September 2009, 11:41

OK then, I made the assumtion that people knew the engine should be operating within the WOT range which on some engines is as much as 1000RPM.

JSP · 12 September 2009, 11:49

That's a few flying over my head.

Knitting is looking like a real good hobby at the moment.

Going to be a bit before I get it wet again (chill your dirty mind, need this one out of the bilges), but when I do I take it I see what my RPM is at WOT and check speed (this will be speed over ground, will that be ok?)?

What I'm after more than anything is more grip.

Nos4r2 · 12 September 2009, 11:50

Quote:

Originally Posted by Hightower

OK then, I made the assumtion that people knew the engine should be operating within the WOT range which on some engines is as much as 1000RPM.

That works, but then you're going to have the most economical cruising speed/RPM with the prop that gives you the highest top speed-unless you can find a prop that slips significantly less at cruising RPM.

JSP · 12 September 2009, 11:51

Quote:

Originally Posted by Nos4r2

That works, but then you're going to have the most economical crusing speed/RPM with the prop that gives you the highest top speed-unless you can find a prop that slips significantly less at cruising RPM.

I'm off to join http://www.knittingforums.co.uk/

Nos4r2 · 12 September 2009, 11:52

Which... (to answer JSP's last post) means trying lots of props out 'til you find one you're happy with...

chewy · 12 September 2009, 11:57

Quote:

Originally Posted by Nos4r2

Which... (to answer JSP's last post) means trying lots of props out 'til you find one you're happy with...

Thats a good incentive for him to get it finished sharpish!

Hightower · 12 September 2009, 12:04

Quote:

Originally Posted by Nos4r2

That works, but then you're going to have the most economical crusing speed/RPM with the prop that gives you the highest top speed-unless you can find a prop that slips significantly less at cruising RPM.

Not in my experience of comparing two props on the vipermax.

It originally came with a 21" which was running towards the bottom end of the WOT range.

I bought a 19" off of ebay and tried this. Whilst giving me any more Top speed at WOT is actually gave me less speed at 3000rpm. If memory serves me it was about 3 knotts different. They where back to back trials in the same sea conditions.

No serious difference in acceleration either.

So with 2knotts faster speed at 3000rpm and 250RPM lower WOT I'd have to deduce that I'd be getting more miles per gallon at my usual cruising speeds with the 21"er.

Hightower · 12 September 2009, 12:07

Quote:

Originally Posted by JSP

I'm off to join http://www.knittingforums.co.uk/

But before you do visit that website, you could visit the Prop thread and see if you could borrow a few different sorts from there first.

Hightower · 12 September 2009, 12:07

Are you comming to the Searider cruise next month JSP?

JSP · 12 September 2009, 12:09

Quote:

Originally Posted by Nos4r2

Which... (to answer JSP's last post) means trying lots of props out 'til you find one you're happy with...

No don't say that! That sounds like the expensive word....erm..which is expensive.....

I'll be happy with more grip to start off with, so (and I've no idea which way to go) I'll try a 21"?

Anyone want jumper for xmas?

JSP · 12 September 2009, 12:10

Quote:

Originally Posted by Hightower

Are you comming to the Searider cruise next month JSP?

I am mate, but not with my boat. Wont be finished by then