Volvo Penta 280 leg (or more accurately prop)

[ontheplane]

Dear All,

My "engineers" on the 'new' boat have decided that my running problem on the engine is mainly down to the prop being wrong.

Now I know it is overpitched, but I would dearly like to test their theory before throwing away £250 on a new prop....

I have a Volvo AQ145A fitted to a 280 leg in a Fairline Weekend 21'

The original prop was (to use a technical term) f**ked....

I picked up another with a 19" pitch at a decent price however this seems far too high and the boat won't plane nor rev over 3000 rpm, it just dies.

My "engineers" (I use quotes as I am not convinced they could engineer their way out of a paper bag) reckon it dies as it becomes overfueled - however I would suspect that if this was the case it would stall not just drop back to 1000rpm until I closed the throttle.

Anyhow - the symptoms are...

Engine revs cleanly up to about 2000 rpm increasing boat speed in a normal manner, but doesn't seem to want to go any faster as the revs rise to 3000 rpm. (I suspect at this point it is trying to get over the hump but can't (Lack of power). Opening the throttle any further than that causes the rev's to die totally back to about 1000 rpm and they won't rise again until you throttle back to just over tickover. Opening the throttle quickly causes engine to die back to 1000rpm.

I guess my question is twofold:-

1) Any ideas what it might be

2) Anyone got a 13" prop for one of these legs (I think it is the Short Hub type - I don't actually know how to tell) I can either
a) Borrow
or
b) buy so cheap that I don't mind if it doesn't solve the problem
or
c) Buy on a sale or return basis
d) Know where I can get one of those Piranah props (they do make them for the Volvo) at a sensible US type price (us$130) rather than the UK£190 that they seem to want over here.

Thanks all

 

[BarryH]

I'd be looking at a pitch of 16/17 inch for your boat. An inch of pitch equaites to roughly 500 rpm. It does sound like the boat is struggling to get onto the plane. I'b be inclined to start a with a 16" prop. Forget thos piranah things, they're next to useless. I got caught out with those in the past. 130 odd horses thru a plastic propeller!

The fueling thing is possible but I doubt you'd over fuel to an extent that it'll flood especially at 2000 rpm. Maybe, I couldn't be sure without looking so its just something to check, the fuel pump might not be dleivering the fuel required at those revs. Just a thought. I take it you've checked cam/ignition timing etc.

Talk to the likes of steel developments re a new prop. They could re pitch yours but only by an inch.

It won't be blisteringly quick with the 145 as it only puts out around 138 horses. I would check what setting you've got the trim pin on in the transom shield. I've the same engine set up in a 21' Tremlett. It will only just push the low 30's on a good day.

 

[ontheplane]

Thank you.

I am not sure going from a 19" to a 17" pitch will be enough - hence the request for a 13" (I would try a 15" tho).

I have had the fuel pump replaced and am hoping that will cure the problem, although why that would cause the engine to die rather than just not go any faster is a mystery!

Piranah supply props for engines up to 300HP and they "claim" that the plastic flexes less than the Ally - don't know if that is true tho.

Thanks for your reply tho - will give steel dev a call

 

[BarryH]

13 inch will be too low. It'll over rev like billyo. The engines peak revs are 54-5500 rpm. The 13 will let the enige over rev to easily. Start with a 15 at the very least. Bearing in mind that once the boat gets on the plane the revs will rise very quickly.

Do check the trim settings on the leg tho. Get it set so the cav plate/exhaust is level and in line with the keel. If you can get it so the leg is set with the trim just out then that'll be better once on the plane. Its a bit of a compromise as you need the leg in to get on the plane easier and once there, out for an easier boat trim for speed etc.

But don't go as low as a 13. It'll rev the nuts off it. Forget the "claims" I had one on a four cylinder mariner. It was pants at best and a total waste at worst. Made nice omlettes tho!

 

[oldgit]

Boats and Outboards web site has got some s/h long hub 280 props or Coastal rides will sell you a new one for 140.00 ,or failing that Steel developments will repitch AND rebuild your old prop for around 50 quid.Bung em another tenner or so and get it back in 3 days.

 

[BarryH]

Actually, just to add, Give SD a ring and tell them what boat you have its rough weight length engine etc and they'll give you the, near as damn it, right prop.

 

[studgies]

We have found Sealine themselves very useful in the past, call or mail them the hull number and they'll look up the original prop dimensions and pitch for this boat.

 

[studgies]

please ignore the above, Jim misread Fairline for Sealine....it is his age!

 

[ontheplane]

Thanks all,

Will certainly give SD a call and Coastal Rides too - we'll see what happens!

Think I will aim for a 15" pitch unless one of these guys have a couple of sale or return props so I can try both. I want a better pull out than top end as I would like to tow a wakeboard - although I really don't think it will be powerful enough to do so - perhaps a watertoy will be the limit.

Anyone here got an old Short Hub 15" (or 17") prop for a 280 leg they would be willing to offer on me having it to try - will buy if it works!

 

[[2068]]

The prop might be part of the problem, but it sounds like there is something else wrong. A correctly set up engine if overpropped should just "sit" straining, not getting planing, (until it explodes), not drop back to low revs.

I don't know that particular engine that well, but check the advance mechanism, check the carb, coil, etc. I'd be really surprised if the prop is the only problem, although a 15"-17" sounds about right.

dv.