Limited Revs - any pointers please?

[TelP]

Quite new to boat ownership and apologies for my first post being a question.
Fairline T29, 1997 with AD31P-As 150hp. Very little on the hull or outdrives. Ran 2 weeks ago to 20knots comfortably up on the plane. Over the weekend we couldn’t get the engines to pass 2500rpm. Tried multiple trim combinations.
No smoke.
PSi 60 on both engines. No over heating.
Refuelled from half to full tank before the 12nm journey.
Both props turn by hand in neutral.
Both engines rev past 3000rpm when disengaged.
No sign of anything tangled in props.

Checked my levels and sea water filters before the weekend.
Plan on checking fuel on Friday for water and bug but my own logic says that it’s unlikely to come from a reputable fuel supply in our marina.
Has anyone experienced anything or any clues please?

 

[volvopaul]

Quite new to boat ownership and apologies for my first post being a question.
Fairline T29, 1997 with AD31P-As 150hp. Very little on the hull or outdrives. Ran 2 weeks ago to 20knots comfortably up on the plane. Over the weekend we couldn’t get the engines to pass 2500rpm. Tried multiple trim combinations.
No smoke.
PSi 60 on both engines. No over heating.
Refuelled from half to full tank before the 12nm journey.
Both props turn by hand in neutral.
Both engines rev past 3000rpm when disengaged.
No sign of anything tangled in props.

Checked my levels and sea water filters before the weekend.
Plan on checking fuel on Friday for water and bug but my own logic says that it’s unlikely to come from a reputable fuel supply in our marina.
Has anyone experienced anything or any clues please?

Is your boat called slow hand ?

 

[jrudge]

150hp x 2 is not a lot on a 30 odd foot boat.

You say there is "not a lot" on the hull or drives - but I would imagine there is enough to cause an issue.

My T40 would not plane with dirty props.

If a boat is not performing etc then the only place you can start is clean hull / props / stern gear and then go from there.

 

[James L]

Quite new to boat ownership and apologies for my first post being a question.
Fairline T29, 1997 with AD31P-As 150hp. Very little on the hull or outdrives. Ran 2 weeks ago to 20knots comfortably up on the plane. Over the weekend we couldn’t get the engines to pass 2500rpm. Tried multiple trim combinations.
No smoke.
PSi 60 on both engines. No over heating.
Refuelled from half to full tank before the 12nm journey.
Both props turn by hand in neutral.
Both engines rev past 3000rpm when disengaged.
No sign of anything tangled in props.

Checked my levels and sea water filters before the weekend.
Plan on checking fuel on Friday for water and bug but my own logic says that it’s unlikely to come from a reputable fuel supply in our marina.
Has anyone experienced anything or any clues please?

When you say you hit 20 knots 2 weeks ago, what revs were you hitting then?
What speed are you getting at 2500rpm?
If 20 knots was max speed, then it seems to me like you were only just getting on the plane, wouldn't take much (like your extra half tank of fuel) to prevent you getting over the hump.

It sounds like you already had a problem, I would expect 2 x 150hp to be pushing it to much more than 20 knots.

Try running on each engine separately and see if there's a difference between them, it's unlikely both would have a matching problem.

 

[TelP]

Is your boat called slow hand ?

Hi Paul. Yes it is. You know it well.

 

[TelP]

Hi James.
Thanks for answering. We’ve often gone over 20. 24-25 is as far as I’ve taken her. I’m aiming to take her out with only 2 aboard on Fri or Sat and see what a difference it makes. Another good friend has suggested that it could simply be the 4 heavy ppl aboard plus the weekends victuals, full fuel and water.
Will check fuel as well and start from there.
I guess I was hoping that someone might say “I had that and this solved it”. ?

 

[volvopaul]

Hi Paul. Yes it is. You know it well.

I do , I’ve done servicing and engine out in last 2 years .

Your problem hasn’t gone away , it had this problem when a previous owner had it , I advised him on it , then he put it for sale and it did exactly this on the sea trial hence the boat was rejected .

I was told by broker the problem had been rectified, it clearly hasn’t been .

 

[TelP]

I do , I’ve done servicing and engine out in last 2 years .

Your problem hasn’t gone away , it had this problem when a previous owner had it , I advised him on it , then he put it for sale and it did exactly this on the sea trial hence the boat was rejected .

I was told by broker the problem had been rectified, it clearly hasn’t been .

Hi Paul. Are you prepared to let me know what you found please?

 

[volvopaul]

Hi Paul. Are you prepared to let me know what you found please?

I’ve just checked my diary , this was over 2 years ago so could be anything from blocked filters to an engine issue internally, as far as I am aware the problem was never investigated, certainly not by me so I cannot advise what the problem is .
You would need a sea trial and knowledge of what service history has been carried out since 2017.

 

[TelP]

Thanks Paul. We’re aiming to sea trial today. Will let you know what we find as it could be useful to you for reference. Hoping it’s filters.

 

[volvopaul]

Thanks Paul. We’re aiming to sea trial today. Will let you know what we find as it could be useful to you for reference. Hoping it’s filters.

You employed an engineer to sort it ?

 

[petem]

Thanks Paul. We’re aiming to sea trial today. Will let you know what we find as it could be useful to you for reference. Hoping it’s filters.

Good luck Tel! Unfortunately these irritations are an occupational hazard of owning an oldish boat but you shouldn't get disheartened yet, as per our previous correspondence there are planet of simple things that could cause this issue. At least its not bellowing smoke or overheating.

 

[volvopaul]

Good luck Tel! Unfortunately these irritations are an occupational hazard of owning an oldish boat but you shouldn't get disheartened yet, as per our previous correspondence there are planet of simple things that could cause this issue. At least its not bellowing smoke or overheating.

I’ve known this boat for a few years , it’s had the same issue all the time , no owners invested in a cure despite my advice on where to go with it.

 

[Robert Wilson]

I had exactly the same problem last year, albeit with a single 13HP Kubota (raggie stand-by power )

After all manner of attempts to remedy, I eventually (on advice from another forumite) replaced an injector.
BINGO, perfect - everything back to normal.
As a precaution I renewed the other injector as well.

May be worth a try looking at yours.
Good luck

 

[chillee]

Encountered similar issue on my single ad31p last weekend. Cruising at 20kts 3600 rpm and then suddenly start to loose power and revs dropped to about 3300 and WOT. Wont get above that now.
My engineer is looking into it. Hope it's not too serious.