Props aint Props

[Woody]

G'day fella's,
Just chasing some advice I banged my prop up on a rock in dirty unfamiliar water. The boat is a Quintrex Hornet trophy 435 with a Johnson 50 hp 2 stroke. As I bought the boat 2nd hand I don't know if the prop is genuine original or not. It has the markings 2 1/4 x 15 on it . I also tow the kids around on a ski tube. Should I just get the same prop or what ? :-/

Wade [smiley=huh2.gif]

[NQCairns]

Does your boat have a Tacho? if so what was the wound out full throttle RPM with kids, mum, fuel and all the other stuff you pack as typical?nq

[blaze]

If You go to the solas.com.au site they have a link on the LHS of there page that you fill out all details of boat motor and uses and then you get a reply from solas props as to the best suited for your application, not sure if they email you or it auto generates the answer.
Had the same problem this morning my self and emailed solas, they allso have an 1800 number on the website. your cost will be about $300 for a ali prop 3 or 4 blade
They also list repairs for $75
check them out
I think I will repair my old one and keep as a spare and buy a new one
happy rock munching
blaze
ps
feel a whole lot better now I am not the only goose

[buggerit]

I did the same to my 70 Tohatsu while in the Territory so that makes 3 of us .

[blaze]

looking at the solas site this morning and could not find an 1800 number but the normal numbers are there,musta been something in the water when i was looking before
cheers
blaze

[Woody]

Thanks fella's, hey nq about 5500rpms cruising with the usual fishing gear , esky, 3 adults etc but when towing the tube 2 adults on board and 1 in ski tube it maxes out at about 5 grand. I have a foil fitted to ob and I'm told it is the reason she cavitates when turning with a load on. I know she's not a ski boat but it's a better fishing boat than a ski boat would make. This was how I convinced the minister for finance at home.

Wade [smiley=argue.gif] [smiley=2thumbsup.gif]

Wade

[NQCairns]

Wade you would probably find an extra 200 RPM would make the family fun days better (holeshot, throttle response) also the fishing days but less so.
If propped well a foil is usually not needed, some cavitation/ventilation on medium turns usually confirms the motor is at the right height for a fishing rig but a foil confuses the issue, if it were mine I would go down 1 size finer in pitch even 2 sizes but it might be too much on such a light weight and flat hull, One size should make for a better rig and you happier with it IMHO. nq

[keen_as_mustard]

I also have a 435 hornet (1999 model) - just checked my prop and it is also a 12 1/4 x 15. I am contacting Solas as I think my boat should go a little better than it does - currently tops out at 27 knots and pops out of the hole reasonably okay, but the prop seems to spin with no speed increase from 5000 to 6000+ rpm. Admittedly my prop looks a bit worn on overall diameter and the leading edges. I aslo run a foil but will be testing without once I get a new prop.

Have heard the right prop on hornets makes a huge difference - any advice greatly appreciated. I will post advice from Solas when I receive it.

Marty

[Woody]

Forgive my ignorance nq but when you say 1 size in pitch do you mean 12x 15 or
11 1/4 x 15 . I have contacted Solas by email but haven't heard back yet. Also can you tell me how to convert knots to kph .
Marty you said your boat tops at 27 knots. Mine tops at 43 kph at around 5500rpm but I'm not sure what that is in knots.
Thanks again for your advice fella's it's much appreciated.
Wade

[NQCairns]

Wade the last number is the pitch and first is diameter, the fastest way to go down one is to go up one in diameter then down two in pitch but it gets messy that way.
You may only be able to find a 13 pitch prop for your engine, may cause problems on such a hull as yours or it could be simply brilliant (my guess ::) and it is a guess), if your boat has the habit to #porpoise ask for one with a bit of rake to add bow lift at speed.
I am no prop guru, I only know the basics from years ago playing with a couple of race boats and a fast ski boat plus a fair few glass fishin rigs it was a lot of fun at the time. A 50hp hornet is somewhere I have never been, the paid prop experts hopefully will steer you better than I could.
Just a thought, you could go to a SS prop, by design they grace you with performance about an inch lower in number than a aluminium if the specs on either are identical. hope you get there and interested to hear of your experience, like learning this stuff.
43kph = 23kn
cheers nq

[Woody]

Thanks nq, what is the formula for the conversion?
If I go with the s/steel prop I would probably invest in a guard will this effect much
close to $500 for an s/s.Remembering that most of my boating is in fresh water river system {rocks/stumps etc}
Wade

[bay_firey]

Woody
If my memeory serves me 1 Knot = 1.82km

[Morlers]

Woody
According to my conversion calculator 1 nautical mile = 1.852 kilometers thus I would assume 1 knot = 1.852 kph.

Trust that helps

:) :)

Morlers

[Barrymundi]

Marty,

Solas prop for my old Hornet made a huge difference. The first one was crap though because they didnt read it was for a hornet. Returned it and they recupped it, worked well

Al

[NQCairns]

Hi Wade, I have read where some guards claim an increase in thrust above what they take away in drag :o something to do with the way they capture the outer edge of the prop or something.
If you decide on a ring that doesn't make that claim, IMHO look very seriously at a 13 pitch, can you find anywhere that will 'buy/try/swap' props?

[keen_as_mustard]

Al,

Was your Hornet similar to mine and if so what size/pitch prop did Solas provide you?

I am still awaiting a reply from them - probably still on Xmas holidays?

Marty

[Woody]

nq,
I got a reply from solas [ Steve Evans] but it wasn't too helpfull I may have to ring them . He wants to sell me the same prop 12 1/4 x15 compression cast. But he didn't really offer any alternatives in pitch or diameter. I'm interested in what Al's got on his boat. But I think I'll install a guard I don't think I've hit my last rock. I'm also wondering about the foil. My boat needs a wheel alignment ? something fierce I can't let go of the wheel and it's always been that way.
Wade ??? ???

[blaze]

Hi woody
To fix that problem you only need to adjust the little fin above your prop. mark it before ya move it, doesnt need to be moved very far. wheel alinement done
cheers
blaze

[Woody]

Unreal , thanks blaze
Wade

[Woody]

G'day fella's,
SOLAS has sent me the new prop C3 X 12.5 X 14 ALcup 3bl with slight cupping. Remember this is to replace a 12 1/4 x 15 I'm waiting for a reply from them as to what the difference will be but my first contact with them they told me I couldn't do better than the 12 1/4 x 15 for my hornet so now I'm confused.
any ideas ???? Wade

[cooky]

heh NQ - sorry to highjack this post, and I'm sure I've asked this question previously, but do you have any idea what my MERC elipto 115 HP 2 stroke 2001 model should rev out to. I took it out yesterday and could only get about 5300rpm flat out - trimmed up a fair bit. Into a bit of chop (small) - can't remember the speed, but most likely around the 60kmh mark from memory. 3 adults in the boat + usual crap.

I have a Vengeance SS prop fitted by the boat manufacturer. Mate said it should rev higher than that - might be over propped. I said I'm happy with it and couldn't be stuffed paying more money to get a few hundred extra rpm. He thought I might be able to swap it though for not much outlay. with who - I'm not sure

[blaze]

My 115 merc 90 m0del is only aboy that
5400 is what the manual said
cheers
blaze

[NQCairns]

Woody, sorry I misssed this post before, how did the new prop go? Did they tell the truth on your first contact?nq

[NQCairns]

Cooky was that your usuall heavey load -if so then yes you are running with the hand brake on.
Blaze did you go anywhere with the prop calc you posted about?

[blaze]

not at this point NQ
Not sure he is running with the brake on, would check with dealer in relation to revs at wot as my service manual said it is to be between 4750 and 5260
cheers
blaze

[Kerry]

5300?. #Mate said it should rev higher than that - might be over propped. #I said I'm happy with it and couldn't be stuffed paying more money to get a few hundred extra rpm....

The choice is yours a few hundred for a new prop or possibly a few thousand more for the motor :o

First you need to actually find out what the WOT RPM should be (do't you have a manual?) and being a 2S prop accordingly to achieve the top end plus. Revs never hurt a 2S but lack of them certainly will.

Cheers, Kerry.

[NQCairns]

Hi Blaze hope it is warm down there, it is up here :P

Those numbers in the manual represent meeting ONLY the governmental requirement to standardise HP output over all manufacturers, they hold in total no relationship to real world operating RPM - trust me on this.

The fact that manufacturers see more parts sales over an engine's corrosion lifetime also counts as to why they are not unhappy with printing those numbers. They willnot kill an engine within the warrenty period in 99% of cases.

Things were a bit wild in the US 20+ odd years ago with manufacurers deliberatly underrating an engines HP so that their 115hp sticker model blew away a 115hp sticker competitors engine. Of coarse everyone then bought the fast brand and that colour brand got a nice fat dose of cudos at the cash register. This was rife between brands.
Your engine on a dyno makes 115hp (+-10%) by regulation at the prop somewhere within that RPM range straight out of the box and may make 125hp+ at 6000rpm if proped to do so.
Once sold and therefore outside of the regs those numbers can only be viewed as bullshit that will harm and cost money in operating costs like fuel (without doubt) and lugging related repairs sooner or later (some get way with it for a 1000hours but rec engines proped well can go 5000+ commonly, if also decarboned everynow and then). cheers nq

PS got a pretty cool prop calc (.xls) on disk. let me know if you want it.

[cooky]

few hundred for a new prop or possibly a few thousand more for the motor

I'm a bit confused. How does the potential for my boat not reving out to 5500 or whatever (couple hundred rpm) damage my motor to the degree of thousands?

I'm assuming your going to tell me it's like operating in too high a gear in your car or running too high a diff ratio. I just can't see this really damaging a boat engine in rec operating conditions. It pops up onto the plane well and seems to do everything else well / easy.

If it will really make a noticeable difference in my normal operating conditions I might consider it. Particularly if more speed (I like speed).

Yes I do have the manual, but I'm a bloke (haven't looked at it)

[NQCairns]

Woody was your original prop also a Solas?

[Kerry]

Cooky, That's what manuals are for ;) reading, highly recommended [smiley=2thumbsup.gif]

Outboards simply have to Rev to max WOT and prefereably the top end (plus) of the rev range. The wrong propellor for the conditions puts a lot of stress on an outboard and more revs are always better then not enough.

Forget this speed thing, speed has absolutely nothing to do with considering props with regards WOT specifications. Speed is a very short sided consideration in this regard, it's not important and when setup correctly if there a few mph drop then so bit it but generally fuel consumption normally improves even with an increase in revs.


Cheers, Kerry.

[cooky]

maybe I should just contact the experts at SOLAS and see

[Kerry]

maybe I should just contact the experts at SOLAS and see

Maybe you should? and while your at it ask them who will pay the bill if ever the engine has a prop related hangover, but I suppose it's probably overly expectant that somebody running 10 grands worth or so of engine would not have read the manual.

Cheers, Kerry.

[cooky]

probably overly expectant that somebody running 10 grands worth or so of engine would not have read the manual.


my cars worth close to 50 grand, and I've never even opened the manual - so I don't think it's 'overly expectant'. ;)

I just expect it to work :o

and this coming from someone who is reasonably mechanical (built my first car).

[Kerry]

Cooky, Frankly your starting to sound like someone who probably shouldn't be on the water, apart from sounding like being a danger to yourself based on past issues your also could become a danger to other people that are obviously one day going to have to help you out.

You do appear to have a very unsafe and dangerous attitude, want to go 50 mile offshore and don't even know how much bloody fuel your motor burns, spinning a prop and have absolutely no idea what the outboard is supposed to rev out to, don't have time to read manuals, "just expect things to work" [smiley=thumbsdown.gif] and would you call yourself a safe boater, I certainly wouldn't.

Cheers, Kerry.

[cooky]

he he ;D ;)

got you stirred up though :-X

if I was unsafe I wouldn't be asking the questions. But yes I like to take risks - it's in my nature.

[cooky]

oh and nugget (or Kerry) if you've read some of my previous posts I mention quite a few times that I;m new to boating. 3 or 4 months from memory.

I'm pretty sure I'm not meant to be an expert immediately. I think I've done pretty well for a few months - thanks to Ausfish and a few friends in the main

[aussiebasser]

Cooky,
If you've ever lifted you cowl off and operated the throttle, you'll notice that apart from carburettor linkage movements there is also a timing advance happening. The timing advance is mechanical and reliant on throttle opening, and full throttle should will give you full timing advance. If full throttle is not producing full revs, then the timing will be too far advanced and could cause detonation and overheating. In reality. This is why under revving has more potential to cause damage than occaisional over revving, a 2 stroke should be able to reach it's maximum revs.
If your's is a 4 cyl, max RPM should be 4750 to 5250, as stated here:
http://www.mercurymarine.com/mercury_115_classic

[cooky]

jeezus - I'd already written a lengthy reply and something happened to the ausfish site or my internet connection.

In brief.

mine is the saltwater series - most likely the same with different stickers http://www.mercurymarine.com/mercury_115_classic_saltwater

I can't understand how I can be doing the engine damage if the manufacturer recommends WOT at 4750 to 5250 and I'm achieving 5200/5300rpm. If what NQ Cairns says is correct how do you know who to believe? I'm assuming following manufacturers rec that I'm doing the right thing by my motor and it's propped well.

black beauty

[Woody]

nq,
The new prop didn't fit well. The bush is too long which made it impossible to do up the castled nut tight enough to get a split pin through. Steve from solas said this happens occasionally but they're gunna machine one down .shit happens I'll have to have a look tomorrow at the old prop I don't know what breed it is. I think I'll get it repaired for a spare though.
woody

[blaze]

From memory
mine boat 20 foot glass
115 merc
wot ? around the 5400
speed 62kph playing with trim
prop 13 x19p solas 3blade
Going to try a 13 3/4 X 15p
Gotta get the leg back on yet after new seals
Real bitch when work interfers with my boatin and fishin, but ya get that
cheers
blaze

[blaze]

Hi NQ
my info come outa my Merc Work shop manual and when I first put it on, got the local mech to check it all and he was happy with revs, I have good holeshot and was happy with the prop set up before damage, may have been cupped a little much.

[NQCairns]

No worrys Blaze I really am only talking rule of thumb (suits 90% of engine models), I have no experience with your particular engine it may be an engine that runs out of puff near 6grand. I know the 6cyl Merc tower of power 115 needed around 5800 to keep them from blowing early but the newer 4cyl may well be proped happily near 5400? I do doubt it but dont go spending any money you wouldn't spend normally based on my recomendations (if your thinking about it) without doing some net research on your particular engine. For curiosity sake I will run your numbers through the calc sometime tomorrow. cheers nq

[NQCairns]

Hey Blaze I just ran a few your numbers (if yours numbers were acurate and my ratio guess is close?), ATM with 19p,62kph,2.0 final drive and 5400rpm WOT you have big slip numbers terrible actually at 21% :o. Your boats size/weight/hull shape/wind resistance is too much for that prop! by a long way IMHO.
If you fit this new prop which equates to about 17p if it were the same diameter as your current prop, it should be a big efficiency improvement (no more lugging), it may spin to 5700 to 5800 and slip should reduce #to under 10% WOT hopefully (cannot get worse!)and you might see 66kph! Your cruise numbers and fuel consumption will be better also, look forward to you getting that leg on, it's all very intersting. nq
PS tell me to shut up any time :-X :D

[Woody]

G'day fella's,
Gave the new prop a workout on Sunday. { C3 X 12.5 X 14 ALcup 3bl }
She seems to get up a bit quicker and I've only lost about 2 kph top end at the same revs { 5500 rpm } I couldn't tell about fuel efficiency though cause we where towing a tube .
woody

[NQCairns]

Hi woody did that prop make any difference to the cavitation? Is the foil still on? do you think you still need it? Why still the same RPM flat out or is it? If it gets up quicker you should have a couple of extra 100s to go above 5500, comparing apples to apples that is. cheers nq

[Woody]

G'day nq,
I've still got the foil on for now, the engine seems to rev up when turning even slightly but the speed appears to increase slightly as well {1-2 k's} is this caused by less drag in a turn ??? the old prop rev'd up but the boat slowed down as though losing traction. You'll have to forgive my ignorance about these things Ive only ever had a 3 mtr tinny before this boat and none of this mattered. All / any advice is appreciated.
woody

[NQCairns]

Woody I dunno, is your foil out of the water when on the plane? Strictly it should be. Possibly the turn causes a dip in the water around the foil and exposes it or half of it? The decrease in drag might do it.
The cav plate has served it's purpose by the time you are on the plane, the hull should be doing all the lifting at this stage so the foil should be high and dry, at least the top with the bottom skimming at worst, your motor may be too low if the foil stays a foil at speed.
Only you know how you like your boat so sucking an experiment for a little while until you get a feel for how much better or worse it is can be worth it.
All that matters is that your happy with any outcome, not what is supposed to be right or wrong.
I hate foils but there has to be a reason most Hornet owners fit them, when you have the time and inclination try a few runs without it.

The placement and amount of cup and a manufacturer put in is very subjective so I have not the first idea what that prop would or should do over your old one ???.
The second best thing to being out in a boat is talking about them, I wouldn't call you ignorant at all, when it works for you, you will know. cheers nq

[Woody]

nq,
I've never really taken any notice where the foil is at speed but I will on the weekend. I do remember someone posting their engine's height details { hole number wise} on a post somewhere and mine is lower than theirs was but thanks for the help I've got some playing around to do.
woody

[Woody]

k

[blaze]

Hi Nq
well the legs back on, test today
prop 13 3/4 X 15
revs 5800
gps speed 54km
holeshot - make sure ya hang on
I think I need to get a 13X 18P
or
a 13 3/4 X 16P which would split the 2 props I have
At the moment the boat still has the 13 3/4 a 15P prop on as it seems like it holds its head better and is more responsive to trim, not so much talking about bow lift but when trimmed correctly there is a good increase in revs, so I will hunt for another prop to try.
cheers
blaze

[NQCairns]

You got a ski boat Blaze ;D ;D
What is your gear ratio?
I reco you are right regarding prop choices, you could get that new one cupped. Have you ran any slip numbers to see where you are at? Its definatly traveling too slow for the rpms you are running, not suitable for a fishing rig.nq

[blaze]

the prop I am on ATM is second hand and the only thing it will cost is a little bit of sign writing on a ute, end up about $5.00 and a little bit of time. I will keep chasing another prop to try (nice to get another for the same sorta deal). thinking about leaving this one on for a trip next week, trolling, start trolling in 100m about a 1km from ramp and head to the shelf or there abouts, about 30km out. Gets a little rugged and the extra power may be a benifit.
The gear ratio is 2.07:1
cheers
blaze

[blaze]

Hi Nq
Using that calc it comes up with 0.152, did i do some thing wrong
cheers
blaze

[NQCairns]

Hi Blaze that prop was a bargain, I ran your numbers also but got slightly different I got #0.1570, just multiply by 100 for % so 15.7% slip which is still fairly high. Has that prop been filed? or it might be a very low cup compared to your last one because it should have a heap of extra surface area per inch of pitch over your old one being 3/4 inch wider overall, possibly more cup would help I dunno, good luck with a marlin? (you will have to polish your prop :D) nq

PS you may allready know but a general rule of thumb is:
1 inch larger diameter = 2inches extra pitch and a typical cup job = 1 inch extra pitch. cheers

[blaze]

NQ
have ya had a go at cupping a prop, figure that if a template was cut after the first blade is cupped they would be pretty close for a test, whats your thoughts
cheers
blaze
ps
any other comments also welcome
I kwow
just hit it with a BIGGER hammer

[NQCairns]

Blaze do it!! I love experiments. I have only taken dings out so I could follow the general shape either side of the job.
You have some resin and chop strand, would make a good original template and after cup comparison template.
Although how much cup on prop = 1 inch screwing through the water with 0 slip? Good luck with it if you give it a go. Take some photos ;D cheers nq