speed on my S37 - 20% improvement!

[Elessar]

Have had trouble getting optimum speed out of her. She spent most of her life on the river before I took her out last year.

A bit of hard use and a good service saw 19 point odd top end improve to 24 point something, but I knew she still wasn't right. The air filter made the biggest single improvement.

Merc 220s with Bravo 2 legs and 23" props.

I was getting up to 3900 RPM at WOT.

Last week I coppercoated her (she was clean and didn't even need a jetwash so fouling wasn't the problem)

And I increased the pitch of the props to 24". (thanks JRB)

result - a 5 knot improvement to 29.5. It's a shame I couldn't have made 1 change at a time as it would have proved the impact of each change, but with the cost of lifts that was out of the question.

But I'm still hitting the 3900 RPM so I think there's still a little more to be had. I'm going to get the props cupped and see what happens - unless anyone can lend me a pair of 25" bravo 2's for the weekend???

BTW I checked with (the always incredibly helpful) Sealine who said she was fitted with 23" as standard when built.

Any experience of prop sizes/performance on this boat or other comments very welcome.

 

[Sneds]

Amazing what a good suply of clean fresh air can do.

Must change my air filters, they only cost a couple of quid and can easily be overlooked.

 

[davedpc]

What type of air filters do you have. Are they the washable foam sheet type? Im sure the 220 are designed to run at 3600 wot as there quite a tourquy engine. The standard bravo 2 props i think are already cupped which is equiv. to 500 revs. over non cupped. You cant get an ally prop. from a non patent supplier so a new one is about £400. My F33 with the same engine and props will wot at 29.9 knots with a clean botty.@3600.

 

[Elessar]

That's very helpful thank you.
Yes they are the foam filters.
I thought 3600 was correct and you have confirmed this. My readings are from the uncalibrated dash tachos. The no load rev limiter cuts in at 4000rpm on these tachos - would that make it a correct reading?
I have navman fuel flow meters which have the ability to fit an accurate rev counter which I will install on the weekend. Then if I am reaching 3900 it looks like I need to go to 25" props.
Do you really mean 500 revs? I thought cupping was equivalent to about an inch which equals about 200?
I presume the F33 is about the same ish weight as an S37 so the speeds probably similar - so I doubt I've much more to gain speed wise but for engine life reasons it would be nice to get the revs right.

 

[Nick_H]

I could get about the same speed (29.5 kts) on my S37 with AD41 volvos (200hp), so i'd expect you should still be able to find another knot or two, maybe three with slippery coppercoat on its bum. Great progress though, 10 knots extra already

 

[davedpc]

You may be right on the 500revs. Give Streamline Props. a ring at Aldershot 07776014285 . He is the local guy for props. and he rebuilds and sells them like new for about half price. He might lend you a set. One advantage of Bravo 2 props. over volvos is that they dont wear down thin and unless damaged will last years. Mine are original from new 1997. Or try the barge at the riverside boatyard Bursledon by the bridge for masses of s/h gear.

 

[DavidJ]

[ QUOTE ]
I could get about the same speed (29.5 kts) on my S37 with AD41 volvos (200hp

[/ QUOTE ]
Just to add a bit more data, I get 32 knots (GPS) from my S37 with KAD 43's (230hpx2) with a clean bum

 

[Elessar]

Nick, Dave and David. Thank you all. It's all pointing the same way and it seems I will get a bit more out of her yet so I'll keep tweaking.
Baffling that Sealine fitted her with 23" as standard - I don't exactly skimp on my inventory so she's not light.