[Mako]

Hi,
New to the forum and a new Predator 160 owner (1st trip BH Mon) boat is fitted with a Mecury 50hp efi 4-stroke but would not pull more than 4,500rpm for about 22knots, with the throttle on the stop.

3 on-board, gear and food for a days fishing.

I had expected it to be quicker with this load on, am I expecting too much, am I over-propped, its a 2-year old package but very clean was supplied from new with the engine package to the previous owner.

Any views appreciated:g:
Thanks
Tony.R

 

[Dave.S]

Hi Tony

Welcome to the forum.

I have a 60hp Mariner, same as a mercury, and the max WOT is 5500 to 6000 rpm.

I would suggest you are over proped, have a look at the prop it should show the diameter and pitch on it or even the part number. Once you can tell us that info it will be easier to advise what size to go for, be warned that props can be exspensive so don't rush out and buy one that might "just do"!

Dave
:g:

 

[ChrisP]

Rough rule of thumb, 1 inch decrease in pitch adds 200 rpm to the top end.

Pitch calc program here to download.

http://www.castlemarine.co.uk/pitch.htm

You need to put the right information in to get the right prop result out.

 

[Davy Holt]

Hiya Chris,

Is that rule of thumb valid for all props or only outboards ??

 

[ChrisP]

Works on them all mate, it is roughly right whatever the engine, afterall the prop doesn't care where the power comes from, inboard or outboard. I used to work at a prop shop and it was a rough way to check the more accurate calculations when repitching a prop.

 

[Davy Holt]

Hiya,

cheers for that.. I've suspected for a while that my Starboard prop was the wrong pitch, at the same throttle settings it runs 400 revs faster than the port engine and uses less fuel than the port engine. There is also a noticeable difference in thrust of each prop when you use them individually.

 

[MarieK]

Mako can you achieve max revs when you are in the boat on your own and no gear?

 

[ChrisP]

I am guessing you are on bronze props Davy, they have the size stamped on the hub, first number is diameter, second is pitch. Sounds like you have mismatched props. It is not uncommon for a bronzie to have it's pitch altered and there be no amendment to the numbers on the hub made. There is no easy DIY way to check the pitch that I am aware of either.

One of the local charter boats brought his props in as he had damaged them when I was at the prop shop, we found the pitches were different so we matched them as well as repairing the damage. The skipper phoned and told us that he had always thought one engine was more powerful than the other.

 

[Mako]

Mako can you achieve max revs when you are in the boat on your own and no gear?

Hi,
Thanks for all the replies, have not been out single handed, have been out two up with no gear for a very short run but even then did not achieve much more rev wise (no GPS then so no speed).

I will paddle out to the boat and have a look at the weekend, get prop size and run the calcs etc, post fidnings.

Cheers all
Tony.R

 

[Mako]

Quick update, had ashort trip out yesterday very lightly loaded, and unfortunatley without GPS, but slowley opening throttle, revs increased to 4,200 on guage, then apply mre throttle, engine note changes and sounds like revs are going up, needle stays at 4,200. So could this be a rev counter issue ?

Only ref I could find on the prop was a long part no. and a 14P

Cheers
Tony.R

 

[Dave.S]

Hi Mako

My 60hp mariner has this number on the prop 48 73136 A40 13P

Turned out to be a Mercury Aluminum 3 blade 10 3/8 Dia x 13 Pitch

So sounds like you have a 14 inch pitch prop, is the number 48 73138 A40 14P?According to me is a 10 1/4 x 14 pitch.

Drop down an 1" pitch and slightly the diameter and I think you will see a huge differance, even better get one to try first.

Don't forget that a new engine will need time to run in correctly, I saw a big change after 50+hrs running time, most will need 20 - 30 hrs.

Regards

Dave

 

[Happy Dude]

Hi,
New to the forum and a new Predator 160 owner (1st trip BH Mon) boat is fitted with a Mecury 50hp efi 4-stroke but would not pull more than 4,500rpm for about 22knots, with the throttle on the stop.

3 on-board, gear and food for a days fishing.

I had expected it to be quicker with this load on, am I expecting too much, am I over-propped, its a 2-year old package but very clean was supplied from new with the engine package to the previous owner.

Any views appreciated:g:
Thanks
Tony.R

hi,

a mate of mine had a seahog seatrooper which is roughly the same weight as the predator if not lighter and he had a 50hp 4 stroke yamaha on it.

his top speed with 3 onboard was 22-23mph so you may well be at your top speed for that engine/boat package.

but i may be wrong, someone will be along to point that out soon no doubt
:clap3:

 

[Norrie]

Hiya, I have a Shortie, (Dont know how it compares in size to the Predator) with a Mariner 50hp 4 stroke, 3 up, with all the gear, two full tanks, and a big warp, it does 22-23 knots , not had it on a flat calm yet, so might get another knot out of it, so, I think you might well be at the top end for yours...

 

[Mako]

Hi Mako

My 60hp mariner has this number on the prop 48 73136 A40 13P

Turned out to be a Mercury Aluminum 3 blade 10 3/8 Dia x 13 Pitch

So sounds like you have a 14 inch pitch prop, is the number 48 73138 A40 14P?According to me is a 10 1/4 x 14 pitch.

Drop down an 1" pitch and slightly the diameter and I think you will see a huge differance, even better get one to try first.

Don't forget that a new engine will need time to run in correctly, I saw a big change after 50+hrs running time, most will need 20 - 30 hrs.

Regards

Dave

Thanks, yep that appears to be the prop fitted, although taking your point about hours run I might leave it a bit longer yet and see what happens. Managed to record 24 knots on the last trip, althought the revs still seem to 'stick' at 4,200 which is close on 27mph so very near design speed of the boat (and quick enough for me anyway) economy seems to be very good at a 16knot cruising speed.

Cheers
Tony.R