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View Full Version : Prop pitch on 85 model 25hp mariner



Pete Makra
21-12-2010, 03:45 PM
G'day guys, got a little old quintrex fish nipper (3.5mtr) the other day with a 25 hp mariner (1985 model) on the back. Took it out for a run today to see how she goes & I gotta say, I was a bit dissapointed with the performance. Motor runs well so I thought the 25hp would push it around pretty quick. It goes OK, but I thought it would be better thats all. Maybe I'm askin a bit much of a 25 year old motor.

I spoke to my local marine fella and he reckons the pitch on the prop may be wrong. The prop No is 9/X14F which as far as I know means it has 14 degrees of pitch. The marine fella reckons it should be about 12 degrees. He also suggested I try it without the hydrofoils. Any ideas on what prop should be on this thing? Any help is appreciated, cheers

Forgot somethin, I checked the compliance plate on the boat and it says max hp rating is 15 hp. Fella I bought it from got it off the original owner who told him max rating was 25hp. Just wondering if I choose to repower it, would a new 15hp be the better option and would it perform better due to new motor, newer technology and more than likely the correct size motor for the boat.

finga
21-12-2010, 03:51 PM
When you disappointed what exactly seems wrong?
Top end speed, hole shot, porpoising, lots of spray??

That motor should make the tinny fly.
Probably well over rated size for the boat.

My guess is the outboard does not rev out and is very sluggish getting to the plane as prop is waaaaay to large for the motor and the motor is labouring.

Pete Makra
21-12-2010, 04:41 PM
When you disappointed what exactly seems wrong?
Top end speed, hole shot, porpoising, lots of spray??

That motor should make the tinny fly.
Probably well over rated size for the boat.

My guess is the outboard does not rev out and is very sluggish getting to the plane as prop is waaaaay to large for the motor and the motor is labouring.

Thanks finga, the guy I bought the tinny from got it off the original owner and said the max hp rating was 25hp. The compliance plate actually says a max rating of 15hp. If I choose to repower it with a newer model 15hp, would it perform better considering new motor and new technology, as apposed to a 25 year old 25hp mariner.

Dissapointment wise, it may just be me. I havent been drivin tinny's for about 16 years since I was chasin illegals (fishing boats and boat people) when I was in the navy. Hole shot wasn't great, nor top end speed, not that these are what I'm after. I just want to potter around with the missus and get from a to b in a reasonable time.

The biggest problem I had was actually stayin in the boat (lol). At first, every time I got on the plane I found it hard to keep her in a straight line as my weight (100kg) was on one side and the slightest tiller adjustment caused the boat to tip dramatically on one side. It really seemed that the back end was digging into the water and I basically had to let go of the tiller to stop myself from goin into the drink. Twice, I thought I was a goner and was going to capsize. Beautiful calm weather/water by the way. After a couple of hours though I seemed to be gettin the hang of it again but whenever I opened her up I could tell she wanted to tip over if I made the slightest error. Probably just out of practice but other (albeit bigger) tiller steer boats were zippin past me and didn't seem to be havin any problems.

I had the motor trimmed right in to keep the nose down by the way.

What do you think about re-powering to a 15hp
Did I have the trim incorrect
What about the back end diggin in and tryin to toss me out, I don't think thats porpoising (I'm guessin driver error, out of practice)
Can I change the current prop until I can afford a new moter & if so, what do I put on

All good/dumb questions, but I would appreciate any answers, cheers

finga
21-12-2010, 06:15 PM
I reckon the motor may be too deep and the foil is just playing havoc.
Any pictures??

The motor should be a pearler for that boat.
Nothing wrong with that model of motor for your boat.

Pete Makra
22-12-2010, 07:06 AM
I reckon the motor may be too deep and the foil is just playing havoc.
Any pictures??

The motor should be a pearler for that boat.
Nothing wrong with that model of motor for your boat.

G'day finga, hope this ebay link works as there are a couple of good photos of the motor.
http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=260699655927&ssPageName=STRK:MEWAX:IT

I thought the motor would be a pearler as well. It runs smooth (2nd pull to get her goin, then 1st pull thereafter). No smoke after start up either. With the 14 pitch prop though, she seems to labour. Screams in neutral but can't get there when in gear. Got the day off so might take the foils off and take it for a run. Might see if Google can tell me what prop should be on it and try to get a hold of one from somewhere for now. Cheers

finga
22-12-2010, 08:58 AM
Those old Quintrex's are lengendary.
My dad has a bit bigger one from 1971 still with the original 25hp Envinrude.

The motor is way too low just by looking at the first picture. Other better pictures would really be the decider.
The cavitational plate should be sitting just proud of the water when planing.

If your not happy with the motor...just send her to QLD. I'll even pay the freight :)

Here is a link to Solas props. It'll give you an indication to props that would suit and a call to them would tell you exactly which one you need and then you can look for one.
http://www.solas.com.au/mercury_mariner_mercruiser_3b2.html

STUIE63
22-12-2010, 09:15 AM
+1 to what Finga said but I reckon take the wing off the boat as well before doing anything but she does look low and it sounds overpropped
Stuie

Tailortaker
22-12-2010, 02:31 PM
It is hard to see but as said above the motor looks too low. I run a solas 10.1 x 13 prop on my 25hp.

Pete Makra
22-12-2010, 04:22 PM
Thanks to Tailortaker, stuie63 & finga. Took the foils off and just got back from takin the tinny for another run. Much better handling & didn't have to fight to turn the tiller. The stern wasn't diggin in and tryin to toss me out. Speed outa the hole was crap though and takes a while to plane. One up, you can't see anythin until she planes, but when it does, alls good. I got her up to 33 kph no probs. Although only small, this thing is pretty beamy and a lot heavier than newerones the same size, so maybe I'm expectin a bit much.

Prop is too big and will try & get another one. The motor does seem a bit low but it can't go any higher. The securing nuts are about an inch from the top of the transom as it is. Cheers

finga
22-12-2010, 05:04 PM
That thing should be doing around the 50-60km/hr.
I get more then you now with a 15 on the back of a 3.7m tinny. And I'm a porker :)

STUIE63
22-12-2010, 05:40 PM
it sounds like it is a long leg motor on a short leg transom to me

dreemon
22-12-2010, 08:21 PM
If the motor runs well and good cond, keep it, I had a mariner 92 40hp and bullet proof, 14 p is just too big for your 25 , what you need is at least a temp rpm gauge to help you get the max rec rpms out of it while you test a couple of props being either the 12p or 13p, when I had my tinny I had a 13 and 14p and traded props as needed , on my own id stick the 14 onit. and hit 64 kph

I had to have 70 mm added/welded to the transom of my 06 brooker to get the cav plate sitting where I wanted it, only cost $ 40 so it's not hard to get it closer to what you want or need, then you should get some good hole shot 12p and top speed with a 13,

the 13 will be faster than you 14p,
Cheers

Pete Makra
23-12-2010, 06:00 AM
Thanks to all for advice so far. Gonna try to get a hold of a 12p prop & see how she goes. Wonderin though, where should the cav plate be sitting in relation to the bottom of the boat. Just measured it and plate is flush with boat bottom, with the bottom of the leg 29cm below that.

Does it matter that the cav plate is not parrallel to the keel cause I have it trimmed right in to get the nose down. The plate also has the 4 holes in it from the foils that I took off. Should I plug these up with silicon or somethin. I'll investgate moving the motor up if the prop don't work, cheers guys

finga
23-12-2010, 06:27 AM
Thanks to all for advice so far. Gonna try to get a hold of a 12p prop & see how she goes. Wonderin though, where should the cav plate be sitting in relation to the bottom of the boat. Just measured it and plate is flush with boat bottom, with the bottom of the leg 29cm below that.

Does it matter that the cav plate is not parrallel to the keel cause I have it trimmed right in to get the nose down. The plate also has the 4 holes in it from the foils that I took off. Should I plug these up with silicon or somethin. I'll investgate moving the motor up if the prop don't work, cheers guys
The cav plate should be just out of the water when your planing.

No need to plug the holes and the trim will need to be adjusted again as the bloody foil would have done all sorts of stupid things if it was under water when planing.

If the motor needs to be raised there is another option other then welding the transom (which will require paint then) and that's a jacking plate.
Easy to get and very good to sort this sort of problem out.
Stuie hit the nail on the head I reckon with your motor been long shaft and the boat requiring a short shaft.
Your boat has a dip in the transom and my dad's is straight across the back. His is a long shaft.
Jacking plates can be as simple as this one which is basically two bits of aluminium channel
http://www.iboats.com/mall/image/view/1/6/40130_0.gif

To hydraulic ones
http://www.iboats.com/mall/image/vendor/16/big/40129.gif

Or even something like this that sits on top of your transom and bolted through the existing holes and then your motor is bolted to it.
http://www.iboats.com/mall/image/vendor/16/big/40157.gif

Which ever way you won't need too much too lift it to get excellent performance and welding would be a last resort for me.

STUIE63
23-12-2010, 06:37 AM
Pete here is a really good explanation of setting up the engine height with good photos as well . http://www.veradoclub.com/smf/index.php?topic=137.0
Dreemon is on the money with need ing a portable tacho to get the revs right whilst propping .
Stuie

Pete Makra
23-12-2010, 07:01 PM
Thanks for all the advice guys. That web site was really helpful stuie63. I've run out a time as the missus and i are goin down the coast boxing day for a week of fishin. At least with the foils off I can steer the damn thing easily and hey, with her sittin up the front, we might get up on the plane a bit easier.

I'll have a look at raisin the motor and new props when I get back. Thanks to all and have a safe silly season. Catch plenty OK, Cheers

Pete Makra
08-01-2011, 07:41 PM
Thanks for all the advice guys. That web site was really helpful stuie63. I've run out a time as the missus and i are goin down the coast boxing day for a week of fishin. At least with the foils off I can steer the damn thing easily and hey, with her sittin up the front, we might get up on the plane a bit easier.

I'll have a look at raisin the motor and new props when I get back. Thanks to all and have a safe silly season. Catch plenty OK, Cheers

Back from our trip down south guys. As expected, the little tinny performed like a slug again. No zip and tuff to get her up on the plane. My son & his girl stayed a couple o days with us so all 4 of us went out for a fish & "maaaaate", was it frustrating tryin to push all 4 of us around the estuary and inlet. The speed limited hire tinny's were overtaking us and we actually had trouble gettin past kayakers (man, can they paddle).

Even with just me and the missus, the only way we could get up on the plane was for my lovely to lean as far forward as possible over the bow and for me to stretch forward whilst still controlling the tiller. Even then, it took a long time for the "slug" to build up enough speed to plane.

Anyways, have since been advised that prop pitch for my old Mariner can vary from 8 up to 14, depending on what you want to do. My local marine fella happened to have a similar vintage 30hp mariner lyin around with a 9 3/4 X 9 pitch prop that he leant me to try today. Fitted it and took the "slug" down the river for a test. Pleasant surprise I must admit.

Even though I was on my own, the slug turned into a jack rabbit, jumping out o the water and planing easily. I don't have a rev counter but the motor was reving out nicely, although flat chat I only achieved 35kph with no more revs available from what my ears could tell.

Big drop from a 14 pitch to a 9 I know but there is hope that somewhere between the 2, I will get to where I am happy with. Apparently, the standard pitch for my motor is a 10 & half. Trouble is gettin a hold of some props to test with. Thanks to all for advice so far & I'm gonna try to get a hold of a 10 & a 11 pitch prop to test, as I'm thinkin this will be close to the mark.

Not withstanding the above, we did manage to catch a decent feed every day and had a ball. Cheers again

:)