Engine revs

[KREW2]

I have a Seaward 25 with two 125hp yanmars. If I go on a longish run say 3/4 hours I tend to stick it on 2500rpm. With the bottom relatively clean, lifted out in May, I am only getting 11 knts sog at slack water. Yesterday on a run back from Hamble to Weymouth I increased my revs to 2700. and achieving a speed of 13 knts. the boats is supposed to cruise at 15knts but in order to achieve this I need to run at about 3000rpm.
Both engines have been recently serviced and I had two new turbos put on last year. The engine will rev to 3600rpm. my question is, is it savy to run for a couple of hours at 3000rpm ?

 

[Greg2]

Presuming that the engines pull 3600rpm under load then cruising at 3000 rpm is well within normal tolerances.

 

[Bandit]

With Volvo Penta engines and I assume Yanmar are similar you can cruise at 300 rpm below Wide Open Throttle (WOT).

 

[penfold]

I have a Seaward 25 with two 125hp yanmars. If I go on a longish run say 3/4 hours I tend to stick it on 2500rpm. With the bottom relatively clean, lifted out in May, I am only getting 11 knts sog at slack water. Yesterday on a run back from Hamble to Weymouth I increased my revs to 2700. and achieving a speed of 13 knts. the boats is supposed to cruise at 15knts but in order to achieve this I need to run at about 3000rpm.
Both engines have been recently serviced and I had two new turbos put on last year. The engine will rev to 3600rpm. my question is, is it savy to run for a couple of hours at 3000rpm ?

When you say it's supposed to cruise at 15kts have you previously been able to do that speed at 2500? It's August, so it's quite feasible for fouling to be slowing proceedings.

 

[Portofino]

When you say it's supposed to cruise at 15kts have you previously been able to do that speed at 2500? It's August, so it's quite feasible for fouling to be slowing proceedings.

As well as fouling it depends on the correct prop , previous owners may have messed about .Also with smaller boats the weight , ie has it larded up with cruising stores ?

Just knocking 300 rpm ( or what ever ? ) of WOT is very basic and imho shouldn’t be used .
In the absence of load gauges first see the manufacturers rated rpm at WOT and see if the boat can make it .So here can you ever see 3600 rpm ?

Here‘s mine last Sept ( annual early June ) Med based but the principal is identical.
Rated manufacturers WOT for the engines is 2200 rpm .

I have seen 2276 rpm on launch day after an annual , so it’s about 40 rpm down , but its within spec that’s the main thing .
Overloading occurs across the rev range if it’s overloaded.The only way to tell is to WOT it.Ideally if not mega electronic at a sea trial get a tacho on the fly wheel . But for simple diy “ is it propped correct “ “ is it fouled “ ? Then WOT it and see .

The speeds pretty irrelevant really you need to get see it’s max rated rpm and go from there .If it can’t reach it = further investigation is required .

 

[KREW2]

I managed to get 3400 revs, under load coming home on Wednesday I am not sure if I was at quite full throttle. I will try it when I go out next.
I'm beginning to think it is fouling causing the problem. The antifouling used on the boat from new was Hempel Ocean Performer, which apparently was self eroding, this is now discontinued.
Hempel advised me to switch to a hard antifouling, which would involve total removal of the old paint, or apply two coats of underwater primer to act as a barrier, I opted to go down the primer route. After annual lift out and relaunch in early June I could get 22 knts at about 3400, that has now dropped to 18, a very short time for what may be excessive fouling to build up. I think next year I may get the bottom blasted and start again.

 

[colhel]

I have a Seaward 25 with two 125hp yanmars. If I go on a longish run say 3/4 hours I tend to stick it on 2500rpm. With the bottom relatively clean, lifted out in May, I am only getting 11 knts sog at slack water. Yesterday on a run back from Hamble to Weymouth I increased my revs to 2700. and achieving a speed of 13 knts. the boats is supposed to cruise at 15knts but in order to achieve this I need to run at about 3000rpm.
Both engines have been recently serviced and I had two new turbos put on last year. The engine will rev to 3600rpm. my question is, is it savy to run for a couple of hours at 3000rpm ?

I noticed a bit of choral worm on our stern gear the other day and when I went out a couple of weeks ago I was down on rpm. For the benefit of others, we're moored a stones throw from OP ( I know this because I've thrown stones at him)

 

[Greg2]

I noticed a bit of choral worm on our stern gear the other day and when I went out a couple of weeks ago I was down on rpm. For the benefit of others, we're moored a stones throw from OP ( I know this because I've thrown stones at him)

It seems to be a thing this year on the east coast. We are down on max rpm and speed as are mobo friends in the marina who tell me that some kind of worm has appeared for the first time in our part of the world.

 

[KREW2]

I noticed a bit of choral worm on our stern gear the other day and when I went out a couple of weeks ago I was down on rpm. For the benefit of others, we're moored a stones throw from OP ( I know this because I've thrown stones at him)

Col, you have worms that can sing?
I think you may mean tube worm which is prevalent in Portland harbour. However on liftout this June I did have a bit on Sunset, but I can't see that much should have grown in 10 weeks, but you never know.

 

[QBhoy]

The things to consider here, perhaps, may be optimistic brochure figures quoted, perhaps not taken from gps…
Someone may have changed the props for less pitch, perhaps to suit a previous use in river or inland waterways?
But to be fair…I also think that you shouldn’t worry too much about running her at a sustained 3000 rpm, in terms of mechanical sympathy. Should be no bother to her. Whether or not you enjoy the presumed noise levels, may be another thing perhaps.
Our family has a 40ft princess. I’m sure that has a quoted cruise speed well into the 20 knot window…but I’m not sure anyone would actually run at that speed for any sustained length of time. Suppose each owner will have a preferred cruise speed that both the boat and owner find comfortable to the conditions perhaos. She sounds a lovely boat either way.

 

[KREW2]

Thanks for all the advice, it's reassuring to know that if need be I can run at 2800/3000 rpm for sustained periods. I know the props are original. Sunset was built for the Kimbers who own Seaward boats as a display model for the 2005 boat show. As far as I can see they look like all other Seaward 25 props, and I have had it up to 22 knots in the past. I expect to lose about 4 knots from the top speed after 4/5 months, but this year it seems to have happened in 10 weeks. maybe Copper coat will be the answer.

 

[QBhoy]

Thanks for all the advice, it's reassuring to know that if need be I can run at 2800/3000 rpm for sustained periods. I know the props are original. Sunset was built for the Kimbers who own Seaward boats as a display model for the 2005 boat show. As far as I can see they look like all other Seaward 25 props, and I have had it up to 22 knots in the past. I expect to lose about 4 knots from the top speed after 4/5 months, but this year it seems to have happened in 10 weeks. maybe Copper coat will be the answer.

Fair play. Although I’d perhaps add that it would be very hard to visually differentiate the difference between a propeller of a certain pitch and another of a couple of inches increment either way…at a glance. The stamped details on it would be the indication required to determine. Anyway. You’re likely right by the sounds of it.

 

[scottie]

I noticed a bit of choral worm on our stern gear the other day and when I went out a couple of weeks ago I was down on rpm. For the benefit of others, we're moored a stones throw from OP ( I know this because I've thrown stones at him)

Does this manifest itself as singing propellers

 

[colhel]

Okay, I now know how to spell Coral worm.

 

[KREW2]

So

Okay, I now know how to spell Coral worm.

That'll teach you to throw stones at me.
Sorry, not wanting to be a pedant really, but the notion of singing worms tickled me.

 

[gordmac]

If you are running a Seaward it is worth getting the consumption curves from Seaward. The 25 is as economical at 17kn as 10kn.