Merry Fisher 815 Speed

[FirstMate II]

Hi Folks
Ive purchased a Merry fisher 815 and we are very happy with it as it suits us perfectly, it has a 200hp nanni t4 which was rebuilt after having piston issues (2023)
New pistons gone into it, cylinders rebored, new injectors and a rebuilt turbo . Was given the invoice for all the work that was carried out and it all seems fine.
Engine is running like a dream but under load will not rev up past 3000 rpm ~ 14/16 kts.
It freely revs up to 3,000rpm and beyond when in idle.
Underload it freely and quickly revs & picks up speed to 14/16kts but seems to stop/hit a barrier and will not go beyond it. Clean bottom and prop is not damaged Mabey im over thinking it and thats where it should be but i feel there should be a little more life in it . Any ideas or will i just leave it as it is ?
JK

 

[SC35]

I’d hope you’d get closer to 3400rpm flat out with that engine, 22-24kts.
Cruise 3000-3200rpm 20kts.

 

[FirstMate II]

I’d hope you’d get closer to 3400rpm flat out with that engine, 22-24kts.
Cruise 3000-3200rpm.

That’s what I was hoping . I’d be happy with 18+ , last boat was a antares 760 and she would cruise all day @ 18kts and max out @ 22

 

[kawasake]

I’d hope you’d get closer to 3400rpm flat out with that engine, 22-24kts.
Cruise 3000-3200rpm.

I think your right SC
Delivered an 805 with that engine a few weeks ago
2 hour trip
Making 21 kts at about 3100 rpm through some 2 metre chop on the beam

 

[SC35]

I’m not familiar with that engine, but hopefully others will be along in a bit.

 

[FirstMate II]

Thanks for the replies , could anyone recommend a fix ? Change prop ect ?
Jk

 

[Tranona]

Thanks for the replies , could anyone recommend a fix ? Change prop ect ?
Jk

It does sound like it is overpropped. Any idea what it did before the engine was rebuilt? First thing is to find out what size prop you have and then speak to a prop specialist who will tell you what size it should be to achieve maximum revs. RPM with no load does not tell you much apart from the maximum before the governor stops it at the maximum permissible.

 

[Irish Rover]

Clean bottom and prop is not damaged

How clean is clean. I had a Leader 805 with 260 D4 and outdrive some years ago. I could get 28kts @ 3,600 after launching with new antifoul but it didn't take a lot of fouling to reduce that. If it was laid up in the water for even a few weeks the revs would drop until it was cleaned.

 

[FirstMate II]

It does sound like it is overpropped. Any idea what it did before the engine was rebuilt? First thing is to find out what size prop you have and then speak to a prop specialist who will tell you what size it should be to achieve maximum revs. RPM with no load does not tell you much apart from the maximum before the governor stops it at the maximum permissible.

Tranona , no idea what it was doing before but the specs say 18 cruising and 22 max . Hauled it out last week for a scrub so I got all the info from the prop so will find check that out . Cheers

 

[FirstMate II]

How clean is clean. I had a Leader 805 with 260 D4 and outdrive some years ago. I could get 28kts @ 3,600 after launching with new antifoul but it didn't take a lot of fouling to reduce that. If it was laid up in the water for even a few weeks the revs would drop until it was cleaned.

Irish rover . Very clean went into the water spotless in December and hauled it out last week for a good scrub with very little growth on it

 

[Cill Mar]

Irish rover . Very clean went into the water spotless in December and hauled it out last week for a good scrub with very little growth on it

Hi First Mate, I have an 815 with the same issue, I just took it out for a wash down and the hull is spotless, I had a marginal increase in speed up to 18kts flat out, which as with yours is around 3,100 rpm. I’m having my prop looked at as I I think it may be over propped but wondered if you got yours resolved?

 

[FirstMate II]

Hi First Mate, I have an 815 with the same issue, I just took it out for a wash down and the hull is spotless, I had a marginal increase in speed up to 18kts flat out, which as with yours is around 3,100 rpm. I’m having my prop looked at as I I think it may be over propped but wondered if you got yours resolved?

Hi Cill Mar
I sent our prop away and the lad repitched it to 24 i think . Max 24.5 im sure is what he said . Boat feels a lot better now cruises nicely @ 14Knts at 2500 Rpm and max speed 18Knts 3000 Rpm . Im think this is where they are as the figures i was getting im sure referred to the MF805s and not the MF815 ( Still not sure though )
JK

 

[Fire99]

Hi Cill Mar
I sent our prop away and the lad repitched it to 24 i think . Max 24.5 im sure is what he said . Boat feels a lot better now cruises nicely @ 14Knts at 2500 Rpm and max speed 18Knts 3000 Rpm . Im think this is where they are as the figures i was getting im sure referred to the MF805s and not the MF815 ( Still not sure though )
JK

Out of interest who did you use to re-pitch your prop?

 

[sailorman]

That’s what I was hoping . I’d be happy with 18+ , last boat was a antares 760 and she would cruise all day @ 18kts and max out @ 22

antares 760 and she would cruise all day @ 18kts and max out @ 22, fingers crossed my nxt boat, due to my changed circumstances i thought that the name Caprice would be apocopate

 

[FirstMate II]

Out of interest who did you use to re-pitch your prop?

Used a lad in Wexford called Jimmy Walsh . Great to deal with .
JK

 

[Cill Mar]

Hi Cill Mar
I sent our prop away and the lad repitched it to 24 i think . Max 24.5 im sure is what he said . Boat feels a lot better now cruises nicely @ 14Knts at 2500 Rpm and max speed 18Knts 3000 Rpm . Im think this is where they are as the figures i was getting im sure referred to the MF805s and not the MF815 ( Still not sure though )
JK

Thanks First Mate III, I appreciate the advice, getting the prop looked at on the next service.

Cheers