Help propping boat

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Post Options Post Options   Likes (0) Likes(0)   Quote Gappy Quote  Post ReplyReply Direct Link To This Post Posted: 06 Nov 2018 at 8:10pm
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Jake is the engine hitting the 6k limit easily or takes sometime to get there.

The Suzukis do swing a bigger prop than any other brand with the outset drive shaft.

You are limited on your boat length also as tagit says but if its hitting that limit easy you can easy pitch up and drop back to around 5800 they hate bern way over propped though and just chew gas then also.

Do try a hole higher see if it unloads the engine a bit also you might find you need more bite once it's higher.

Cheers
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 07 Nov 2018 at 7:53am
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Catchalot..
 Sorry Steps I couldn't resist. 

When Jake deploys a million lures, teasers, exciters, dredges, and bibbed minnows, his boat now has the transom dug in and the trolling speed has been reduced by 2.14 knots divided by pie arse root mean squared.

That is a very good consructive point.. like the drag of a low leg  and or permatrim, it is something that would be very difficult to calc unless 2 lots of data are made.. 1 deployed and one not..
Adding a low leg/ permatrim to that, on top of the already loaded engine...certainly doesnt help and if anything makes matter worse when deployed. Its chews right into any reverve power at that rpms.

And yes the prop has a large influence on a displacement hull fuel consumption.. example is a trawler.. if runs short distances to grounds and long drags.. its propped for the drag.
 If long distance to grounds where most of the fuel consumption is its propped for cruise.
 A tug is propped different to a ferry..same hull.

 Bottom line thu.. be it deployed lues or getting to the grounds , both either .. having the engine set up well and correctly propped makes a huge difference to the TOTAL days fuel bill.
 If cant pick it up on trolling can pick up significant amount getting out and back.

 Another curly to note thu...
4 strokes by nature tend to have significantly flatter power to rpm curve at low rpms.. far less reserve power...greater kload on the powerhead...
Also of note: moden 4 Strokes tend to produce a good 10% more WoT power than older motors... to maintain good bottom end power. Thias becomes significant on larger engines ..150 hp plus, not so much under that.
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Post Options Post Options   Likes (0) Likes(0)   Quote jakepitsville Quote  Post ReplyReply Direct Link To This Post Posted: 15 Jul 2019 at 5:16pm
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I know this is quite old but some updates now that the fishing season is over for me its time to get this sorted!

I spent the summer playing about trim and outboard height - As it turns out raising to the highest point available got the cav plate so I could actually see it easily while on the plane and still without any cavitation,  Although the hole shot decreased slightly, this change made the hull perform superiorly while on the plane and handled the sea alot better - the whole boat actually changed - my range of trim control also changed. 

This actually took few goes - thank you for advising this. 

 Interesting the max RMP at WOT (in calm harbour) has gone up is now slightly above 6000RPM about 6050 and WOT brings me to 34-35 Knots with the boat fully loaded vs emptish to reach that before.  

Fuel on the plane has improved abit and cruise is now 20knots at 4100rpm and generally if I am not trolling it is super cheap -  50l for a full day broady fishing  35NM cruising with some hours moving about 8 hours chasing the fish - cant winge at that.

Permatrim has not been removed yet as there are so many holds in the cav plate i dont really know what to do about that.

Still no major change at trolling speed needing to do close to 3k rpm and sucking fuel and difficult to get nose down

 -  I have acquired (cheaply) a 3 blade 14 1/4 /20  stainless prop -  it looks flipping massive and even thought I have seen a suzuki 115 swinging a 14/20 stainless im sure its to big?

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Post Options Post Options   Likes (0) Likes(0)   Quote Gappy Quote  Post ReplyReply Direct Link To This Post Posted: 15 Jul 2019 at 7:30pm
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Jake

Sounds like you are making good progress there.

That prop you have should be fine 3 x14 x 20 is a standard Suzuki size so it's only slightly bigger but depends on blade shape and area also.

We find the engine heights make a big difference what prop are you running at the moment

Cheers
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 16 Jul 2019 at 10:55am
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...me to 34-35 Knots with the boat fully loaded vs emptish to reach that before.

 Give or take, the weight of gear/ ppl etc you have taken out is around the effective weight the low engine had on the hull.


You are now cruising the top end of the range at just over max weight on water.
 That indicates need to go higher in pitch and or diameter (grip) so when the boat is not over loaded it will not over rev.
 IE bring the fully loaded rpms down to mid rpm range.

Going the larger prop.. more grip (at low displacement hull speeds) will help with trolling, and the extra pitch may also.

Throw that prop on, and get some accurate numbers again at best trim for each speed. (rem, increase hull speed the amount of trim can be increased).

From there can calc if require adjustment with slip (diameter) and /or pitch to fine tune.

The permatrim will cause significant drag (fuel economy) at the troll.
 I do not know what effect the holes would have (if any) if it is removed.
If cavitation plate is right height skimming the surface they may cause spray.. which is not good for the engine to suck in. (same issue with low transducers)



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Steps  and others!  Firstly id really want to thank you for the time you have put in to helping me here!  Its one of the reasons why i still keep visiting Fishing.net.nz.

I will put on the prop and test, then remove permatrim and see what affect that has and get some numbers back.  


many thanks again!

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Originally posted by Gappy Gappy wrote:

Jake

Sounds like you are making good progress there.

That prop you have should be fine 3 x14 x 20 is a standard Suzuki size so it's only slightly bigger but depends on blade shape and area also.

We find the engine heights make a big difference what prop are you running at the moment

Cheers

does 14 to 14 1/4 make much difference in area?
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Post Options Post Options   Likes (0) Likes(0)   Quote Gappy Quote  Post ReplyReply Direct Link To This Post Posted: 16 Jul 2019 at 4:38pm
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Originally posted by jakepitsville jakepitsville wrote:

Originally posted by Gappy Gappy wrote:

Jake

Sounds like you are making good progress there.

That prop you have should be fine 3 x14 x 20 is a standard Suzuki size so it's only slightly bigger but depends on blade shape and area also.

We find the engine heights make a big difference what prop are you running at the moment

Cheers


does 14 to 14 1/4 make much difference in area?


Jake

It really depends on the blade shape etc different brands have different blade shapes.

Suzuki have just come out with new props and the same sizing are quite different in rev range vs the old props. When we do a new setup we change props out they Suzuki on prop exchange till we/the client is happy unfortunately you are in the having to buy prop game. I am on holiday at the moment will see what we have at work that might work for you to try when back next week

Cheers
Blair
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Originally posted by Gappy Gappy wrote:

Originally posted by jakepitsville jakepitsville wrote:

Originally posted by Gappy Gappy wrote:

Jake

Sounds like you are making good progress there.

That prop you have should be fine 3 x14 x 20 is a standard Suzuki size so it's only slightly bigger but depends on blade shape and area also.

We find the engine heights make a big difference what prop are you running at the moment

Cheers


does 14 to 14 1/4 make much difference in area?


Jake

It really depends on the blade shape etc different brands have different blade shapes.

Suzuki have just come out with new props and the same sizing are quite different in rev range vs the old props. When we do a new setup we change props out they Suzuki on prop exchange till we/the client is happy unfortunately you are in the having to buy prop game. I am on holiday at the moment will see what we have at work that might work for you to try when back next week

Cheers
Blair


Yeah that sounds good and it's getting annoying now. DIDN'T do enough questioning for the PROP place on TM. The prop I purchased is in ok condition but doesnt fit. Must haVe been for an older 2 stroke and although spine fits good the hub is wrong and is not interchangeable. Darn.
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Post Options Post Options   Likes (0) Likes(0)   Quote Gappy Quote  Post ReplyReply Direct Link To This Post Posted: 16 Jul 2019 at 7:29pm
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Originally posted by jakepitsville jakepitsville wrote:

Originally posted by Gappy Gappy wrote:

Originally posted by jakepitsville jakepitsville wrote:

Originally posted by Gappy Gappy wrote:

Jake

Sounds like you are making good progress there.

That prop you have should be fine 3 x14 x 20 is a standard Suzuki size so it's only slightly bigger but depends on blade shape and area also.

We find the engine heights make a big difference what prop are you running at the moment

Cheers


does 14 to 14 1/4 make much difference in area?


Jake

It really depends on the blade shape etc different brands have different blade shapes.

Suzuki have just come out with new props and the same sizing are quite different in rev range vs the old props. When we do a new setup we change props out they Suzuki on prop exchange till we/the client is happy unfortunately you are in the having to buy prop game. I am on holiday at the moment will see what we have at work that might work for you to try when back next week

Cheers
Blair


Yeah that sounds good and it's getting annoying now. DIDN'T do enough questioning for the PROP place on TM. The prop I purchased is in ok condition but doesnt fit. Must haVe been for an older 2 stroke and although spine fits good the hub is wrong and is not interchangeable. Darn.


Ah bugger

Where are you located up north?

Will check next week what I have.

Cheers
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Post Options Post Options   Likes (0) Likes(0)   Quote jakepitsville Quote  Post ReplyReply Direct Link To This Post Posted: 17 Jul 2019 at 9:29am
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I am up the top near Kaitaia -
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Post Options Post Options   Likes (0) Likes(0)   Quote Gappy Quote  Post ReplyReply Direct Link To This Post Posted: 17 Jul 2019 at 2:15pm
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Originally posted by jakepitsville jakepitsville wrote:

I am up the top near Kaitaia -


Jake sweet that's easy I have a place at Taipa so up there pretty regularly.

Will flick you a message next week.

Cheers
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Post Options Post Options   Likes (0) Likes(0)   Quote jakepitsville Quote  Post ReplyReply Direct Link To This Post Posted: 18 Jul 2019 at 12:27pm
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super!
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 18 Jul 2019 at 12:34pm
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Damn on the hub..
does 14 to 14 1/4 make much difference in area?
 yes..in most cases.. not only surface are but the cupped area,

Small differences like this is wher on fine tunes the rpm/ end use range by adding and subtraction  a few rpms in the WoT rpm range by changing slip %.
By going the higher pitch, that would drop the WoT rpms say 200.. which is still over the mid 5400/ 5500 target.
Going up say another 1" in pitch would be over kill.
Going up 1/4 or 1/2" in diameter will give a little more grip, dropping say only 100 rpms.

When propping, it is important to get the slip (grip) right 1st, on a ball park pitched prop...THEN sort the pitch
I cannot stress how important this is.. when I 1st started messing around things sort of went in circles for a while.. Then all 3 of my mentors (including our own Tagit) gave me that little tit bit. Then all fell into place very quick.
 
Even being able to get  pitch and grip right at the same time once have accurate numbers off a ball park prop and engine correct height.. and built up a data base of boats, props etc, and experience... in that order.

interchangeable props.. that is a big headache.
The basic is spline #, spline Diameter, hub diameter.
Even then one gets stuff like a yammy and jonny/Evinrude. are interchangeable, but may need a little turning down and/ or a spacer.
 
Some Suzuki are interchangeable with johnny/ Evinrude.
Some mercs have the internal hubs that can adapt to different other makes..but they are expensive.

The size/ end use/ weight on water of your boat is sorta on the cuspe between a alloy prop that flexes (changes pitch slightly under loads) and a stiff Stainless.
It will be about cruise speed on flat water the difference will be noticed in data only. Below that, and definitely at trolling you will see no difference.
 The HP taken to turn a heaver Stainless as to a light alloy is only small, but enough to neutralise and differences in data at these loads.
I have my self trailed many cheap  alloy props, suggested ppl to also get a cheap ball park alloy to get intial data....
 Then been able to compare that data with stainless.
Hence why I say you (and our boat ) is on the cusp.
Get above flat water cruise speeds, or start to tow stuff, and there is a definite difference...but not enough to warrant actually going stainless if these loads are very rarely used.

So if a $50 alloys comes up (and local agents tend to load 2nd hand ones easier)
 go for it m8.

What are the exact specs  of the motor prop you are after?
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Post Options Post Options   Likes (0) Likes(0)   Quote jakepitsville Quote  Post ReplyReply Direct Link To This Post Posted: 20 Jul 2019 at 6:30pm
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Wow steps alot of info there. Currently have 14/19 alloy Standard suzuki prop. From all of my reading and research its a pretty average prop.

I've read alot of guys saying a 14/20 stainless suzuki does quite well with a solas not as good. Solas has recommended me a 4 blade 14/19.

The boat needs its bow brought down in lower rpm as it rides high off plane and i was hoping for abit more push lower in rpm for the trolling I do.
Engine Suzuki 2007 DF115 on 5.5 surtees.. It is max size for hull and sits at 6050rpm at wot with a fully loaded boat.
so I was thinking based on reading research and something you said earlier abit more pitch and maybe some cup so 14/20 or 21 or a 4 blade.

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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 21 Jul 2019 at 2:42pm
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We havnt got good data numbers since motor lifted, so anything is hit in miss.
 The old 14X 19 is outside ball park, as the RPMs are over top limit at full load...light load should be at max rpms , full load around middle of the range.

But still close enough to get data to choose a better prop..

The boat needs its bow brought down in lower rpm as it rides high off plane and i was hoping for abit more push lower in rpm for the trolling I do.

This issue is to do with the prop rake.. not 3 blade or 4 blade etc..
 In saying that most 4 blades have a lot more rake...
The rake narrows the thrust cone out the back..this brings the top edge of where that thrust is lost to breaking the surface, closer to the prop.
 When that force is lost the extra balance of thrust, levers the bow up...
Increase rake, narrow the thrust cone , and the bow is levered down, the stern up.Thumbs Up

So yeah a 4 blade with more rake will help out hugely.. with good power as you have , will be a 'new hull'

Going from a 3 blade to 4 blade, means also going smaller diameter.. (even smaller thrust cone Thumbs Up)

And will also help trolling giving far better prop performance/ economy due to better slip numbers while under displacement hull conditions.

Going off good data of a 3 blade to a 4 blade, calculating diameter to slip has a little more guesstimate in it.
 Not have current accurate data....I would recon if the current requirement was say a 14 1/4 19 pitch 3 blade, with reasonable cupping, you would be looking at around a 13 1/2 to 13 3/4 X 19 or 20" 4 blade.

Till have good data of current and or another borrowed prop to establish good slip numbers, everything is just speculative guesswork... except the 4 blade thing.

Do you know if a 2S 2001/ 2005 ish johnny/ evinrude 13 spline prop fits your suzi?


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My suki has a 15 spline so dont think it would fit.
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Post Options Post Options   Likes (0) Likes(0)   Quote MATTOO Quote  Post ReplyReply Direct Link To This Post Posted: 22 Jul 2019 at 5:44pm
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So in reading this post I'm evaluating the value.

To be honest, cost of changing a prop here doesn't show a lot of value.

I think in small boats the benefits are minimal.

That comment is based around style and frequency of use of your vessel.

In the main, a alloy standard prop is most suitable for a Harbour or gulf or day out boatie or fisherman.

If your engine hours per season extend above 300, you crosss bars regularly or beach launch, or troll or have large hours above what I have suggested than there is little point in a change.

If you do, go stainless, and do your calls after a 300 recorded hours so an educated decision can be made.

Otherwise your pissing money and time away.
Just cruising in my now sweetas pimped out Southern 755 HT0!
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Post Options Post Options   Likes (0) Likes(0)   Quote Catchelot Quote  Post ReplyReply Direct Link To This Post Posted: 22 Jul 2019 at 6:45pm
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Small comment from me, an alloy prop will bend and flex if it hits a rock or something hard and generally isn't too hard to fix, a stainless one will not and can smash/damage the gear box big time.

So if you drive around in shallows them think about the alloy softer metaled props, maybe more for divers versus off-shore trollers.
"The sea, once it casts its spell, holds one in its net of wonder forever." - Jacques Cousteau
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Originally posted by Catchelot Catchelot wrote:

Small comment from me, an alloy prop will bend and flex if it hits a rock or something hard and generally isn't too hard to fix, a stainless one will not and can smash/damage the gear box big time.

So if you drive around in shallows them think about the alloy softer metaled props, maybe more for divers versus off-shore trollers.

yes this is a valid point - for small boats that might be launched on a shallow beach and might expect a bit of grounding - an alloy ali prop is better as a 'consumable' than a very hard and heavy s/s one.


No disintegrations!
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