propping issues

[Deiter]

O.K, thought i'd throw this one out there to see how far wrong i am.

Bought a Profish 5.5 plate half cab 6-7 weeks ago, all '93 model. Prettty happy so far, but its not without its issues.

She's got a 90hp v4 vro johnson on the back, and, well, i don't think its big enough. I was just going to buy a new donk, ('bout 115hp) but i thought i would be better off sorting the prop thing out first.

the figures, currently fitted with s/s 13 1/8 X 17p prop, with bugger all weight in the boat.

cruise 4000rpm @ 43kph.
wot 4800rpm @ 58kph.

wondering what size prop i should get to achieve 5500 at wot with a bit of a load on. ( probly 5600 - 5700 w/ no load???)
top speed aint too bad, but she is a slug out of the hole, and with 3 or more on board i have to make sure no one is right at the back of the boat on takeoff or she she stands on her ass and wont quite plane, regardless of trim position. I have also noticed that when on the plane, if i dont trim her right out, it will barely get to 4200 rpm wot.

I know it aint good to work a motor this hard, and i wanna do the right thing by the old girl, as she is in great nic and would barely have 100hrs on the clock.

All input appreciated.

Damo

[mirage]

Call Solas props on the Sunshine Coast. They'll know the solution to your problem.

[blaze]

Have you checked your WOT postion on your engine, engine timing etc, I would do a check on these first.
cheers
blaze

[FNQCairns]

Yeah what Blaze said you have problems way and above the prop alone, you really should get it sorted as your 90hp is behaving like a 60hp.

Your prop should then be OK for near 70kph somewhere above 5500rpm depending on how heavy and well setup your overall rig is (i dont know your hull).


cheers fnq

PS could be anything fuel etc but it sounds symptomatic of a cylinder not fireing.

PPS pull each sparkplug one will be oiled beyond comparison or rusted or both. Hope it's just a spark issue.

[John_R]

I would get hold of a 15" pitch prop and try it.

I recently went from a 17" alloy to 16" stainless and the difference was significant on my 115 Johnson. Now very fast out of the hole, motor holds the revs better and WOT is around 5500.

Agree it sounds like more than the prop per FNQ/Blaze as well.

Regards

John

[Deiter]

cheers guys, always good to get a few opinions.

I agree that it is behaving well below its rated h.p. but i had a mechanical inspection done b4 i bought it, and was told that it looked really good for a motor of its age. Compression is 126-129 psi on all cylinders.
she starts in an instant and blows bugger all smoke. But something is still not right.

will pull the plugs and check wot position tonight.
As far as the wot is concerned, should i just be looking for the butterflys opening fully, or is there more?

cheers, Damo

[blaze]

spaniad king (gary) would be the best on this one. give him a pm
my thoughts would be
carbie sync (all things happening together) along with the timing to be in the correct postion for the throttle postion.
cheers
blaze

[FNQCairns]

Yes and check that the timing advance is sliding all the way to it's stopper, it's under the flywheel.

If you find no mechanical cylinder problem it may be gummed jets in the carby as the midrange and mains act in concert at high throttle settings for fuel supply.

cheers fnq

[Y-Not]

And check thos damn plug leads had all sorts of low rev issues on my old Jhonson when a little corrosion developed on 1 of the plugs dropped a quick 1000 rpm off just like yours seems to have done. Mine was a 115 hp though

[cammac]

hi,

im no expert on props but with regard to motor timing and tuning #i imagine she wouldnt be running smoothly #- ie. some missing #in the rev range somewhere?? - # kind of sounds like #wrong size / wrong pitch prop to me - my 2bobs worth - for what its worth - or maybe the motor is not at the correct height!! #:o
pretty big/heavy boat for a 90??!

Cam

[Spaniard_King]

Damo,

you have a few factors to concider

1. Engine height...is it correct (level the cave plate up with the hull and take a pick side on for us)
2. Engine performance ( At full throttle are butterflys level... timing is a concideration but butterflies will tell most)
3. proppeler size (what are you currently running.. and is it a SS or ally)

Your boat is a little underpowered, most 5.5 sporties that I have worked on run at least a 115 that dosnt mean we cant make this work ;)

Garry

[Deiter]

Righto, plugs look good and all the same colour. :)
Butterflies fully open and synch looks good. :)
Fuel flow is not a problem as i fitted a ditital flow meter, and she doesn't mind a drink (av 28L/hr @ 4200rpm @ 44k/hr) :o

Gave Profish Boats a call this arvo (no build plate, hp rating plate attatched) and spoke to the owner Peter.

He bought th business after my boat was built, and consequently couldn't give me an exact build spec, but he was good and helped me wheret he could.

Max h.p. 125 or 185kg, licenced for 6ppl. load 540kg. cool. good things to know.

He also said that the guy who used to fit the motors never did a water test to check prop performance, height adjustment etc. Just whacked 'em on and out the door. Hmmmm :-X :-X
He reckons mine would be overpropped with a 17" prop. 16 would suit better.
Also said the boat will stand up a bit more on takoff coz the "pod" doesn't go to the hull line

Tooks pics of transom. see attached,

Cav plate is 5-10mm above hull, BUT the keel sits 20mm below that. Its also on the top bolt of the engine bracket. no adjustment there. :'(

[blaze]

lift your motor 2 holes, I reckon you will get a vast improvement. It may cavitate too much going 2 holes and you may need to lower 1 hole
cheers
blaze.
ps
the reason for the lift is that water rises when it exixts the rear of the boat appromately 50mm for every 500mm back from the planing surface.

[Deiter]

further to that,

1) its is a 13 3/8" X17"p s/s prop. original.

2) the bush that slides in the slot and advances the timing as the throttle is opened up has sheetloads of play. timing-advance lever can vary 13-15mm. is this normal??? i have an older omc v4('89) that has bugger all play.

3) I think its just wavering on the edge of being underpowered. 90hp will do. but only if propped down to suit. my 2 cents

Damo

p.s. after checking, the original owners manual says,
"Recommended WOT range; 4500 - 5500 rpm"
That doesn't seem right to me.
My 4 cents now.

[FNQCairns]

That's a heavy looking hull with a decent V also (I assumed a profish was alloy plate for some reason) (by the way what is a profish?) you are simply over propped, no such thing as being underpowered really and within reason, you will just travel slower for rpm but the trust needed at any speed is the same as if it had a 200hp on it.

Consider a slightly smaller diameter prop as well as a shift down the range in pitch but leave the engine where it is for the meantime you may gain 250rpm if you lift it near an inch but small props pushing big boats can be a ventilation headache.

You should reach max spark advance somewhere near 1/2 of full butterfly travel and the converse on backing down, check that this is the case.

cheers fnq

[Deiter]

lift your motor 2 holes, I reckon you will get a vast improvement. It may cavitate too much going 2 holes and you may need to lower 1 hole
cheers
blaze.
ps
the reason for the lift is that water rises when it exixts the rear of the boat appromately 50mm for every 500mm back from the planing surface.

if thats the case, yes, the moter can come up a bit. cheers blaze, didn't know that.

FNQCairns, yep right on all counts. plate alloy built in caloundra. i'll include a pic. The owner , Peter, recommended a step down in prop pitch, as well as having my pod modified to be level w/ the hull. bout a grand. jeez, we're getting serious now. He doesn't build them with as much vee anymore either. bit unstable at rest he reckons, and he is sorta right, but everything is a compomise..

Damo

I think i eventually should fit a 115.

[Deiter]

at da back

[Spaniard_King]

lift your motor 2 holes, I reckon you will get a vast improvement. It may cavitate too much going 2 holes and you may need to lower 1 hole
cheers
blaze.
ps
the reason for the lift is that water rises when it exixts the rear of the boat appromately 50mm for every 500mm back from the planing surface.

I am with Blaze, That engine needs to go up at least 2 holes... maybe 3.. then look at WOT rpm best idea is to get it to cavitate and drop back down 1 hole.

Garry

[Deiter]

at what trim point should it cavitate??

I know that if i trim it up while running i will evenyeally get to a point where i can hear cavitation. At present this is near the maximum trim point, just b4 it kicks into 'tilt'

Damo

[FNQCairns]

Yeah I agree you need to go way up! (must have been spraying heaps) I missed the setback pod - bit unusual and not real common as they can take some extra working out but once done they are superior to a hull extension pod on certain boats.

If you don't spend the money to extend it down you will have a lower planing speed better cruise speed and economy and also a higher top end speed when you do get sorted, on deep v hulls there are almost no disadvantages - it's a half pod right?

Like said by the chaps above and because of the setback go way up unil it ventilates on turns (do you cross bars?) to the point you don't like it. Stay with the same diam but decrease pitch.

You seen pretty clued up on stuff, would be interested to see some figures at each change you do.

cheers fnq

[Deiter]

fnq, it sprays heaps untill i get the trim right out!!!

i had no idea about this issue w/ pods set off the hull line.

[Deiter]

ok. will take her up 2 holes today, but won't get to test till wed or thursday at the latest.
I will take note of speed/rpm/ fuel burn and post back b4 any prop change.

fnq, i haven't crossed any bars in her yet, but its only a matter of time. after all, i didn't buy it to play in the bay.
It doesn't fill me with confidence atm, knowing i need a runup to get going.
In saying that, its not too bad, but still not quite right and i am not too experienced on the bar scene. I have spent the last 7-8 years in smaller boats on the bay (in shocking conditions sometimes) and been outside plenty, but always with other people.

Damo

[Deiter]

ok, took her out for a run a few days ago after raising the donk 2 holes ( still 1 to go).

Basically, it did seem to get out of the hole more smartly, but there was only ,myself and a 4yr old in the boat.

cruise at 4000rpm - I got and an extra 2 kph and fuel consumption down 2lph at optimum trim.

unfortunately, and suprisingly, @ wot there is absolutely no difference. Still only getting to 4800rpm at just under 60kph, and i avoid looking at the fuel meter with the throttle down.

next step will be to get hold of a 16"p prop and see what happens. may even need a 15"p, just guessing.

Thanx to all the guys who replied already
...til next time.

Damo

[Kerry]

The pod has a general rule of thumb of up 1" for every foot behind the stern proper.

The 4500-5500 WOT is right as per the book but you need the top end of the RPM range PLUS, 5600 would make you sleep better.

And what generally happens with a smaller prop, right revs, much happier motor, less stressed motor and better fuel economy.

[julian1]

shouldn't the cavitation plate be level with the bottom of the pod and not the hull ?? raising it a notch or two would be an easy quick test - worth trying

[Deiter]

Kerry ; yes, my idea is to get the wot revs as high as practical. i am within spec as far as the book is concerned, but i think the book is too leniant. much rather have it lazing and go a bit slower than wring its neck for all she got and pull less than 5krpm.\

Julian1, i'm still learning these things too, but to my thinking, the pod could be made at any height above the keel, so that would be too general a statement to make.

One thing i have realised is there are no hard and fast rules. You can get close with a few 'rules of thumb', but it still has to be fine tuned. And rarely do they come fine tuned out of the dealer.

Damo

[Kerry]

Most boats coming out of dealers are generall (as a rule of thumb) over propped to buggery.

Dealers appear to have an obcession with speed but fail to match the prop to the actual intended use. Most times the dealer has fitted a prop that does wonders but basically has little fuel, no gear, no normal fishing crew and all the other bits and pieces that add weight to any boat.

First trip and the dam things almost fails to get out of the water.

When you get the right prop and the engine is singing it will be almost too obvious.

Regards, Kerry.

[Deiter]

Most boats coming out of dealers are generall (as a rule of thumb) over propped to buggery.

Dealers appear to have an obcession with speed but fail to match the prop to the actual intended use. Most times the dealer has fitted a prop that does wonders but basically has little fuel, no gear, no normal fishing crew and all the other bits and pieces that add weight to any boat.

First trip and the dam things almost fails to get out of the water.

When you get the right prop and the engine is singing it will be almost too obvious.

Regards, Kerry.


yes kerry i agree.
Not trying to start anything here either, but it appears that you are saying these boats are lacking holeshot.

Mine has the original prop on it too, so it has NEVER been set up right. :)

[1975fflh]

I dont know if this helps but I have a Coxcraft rumrunner with a 1999 90 HP Johnson on it its a heavy oll glass boat and the Johno pushes her along at about 58kph, according to the Navman gps or fully loaded with 4 people and full 110litres tank and the wifes comfort gear (45kgs I bet) at 52kph.

[a_big_red_1]

Damo, have you tried your new prop yet?
have been reading this topic with interest

Daz