yanmar 315 bravo3

scarab racing · 08-09-2009, 08:28 AM

Hi been trying to set up my yamanr bravo3.

We have tryed lots of different props from 30" down to 24"
The 24's preform the best so far, we have also had the fuel air adjusted to run a bit richer and now get very good acceleration (For size of boat/power) But we are only topping out at about 3300 / 3400 so still looking for about another 700+ revs, any surgestions on gaining extra revs?

Gaining a bit more power with out throwing major £ at it?

Or just drop prop size down to 22"? (any one got a set I could borrow ?)

The power in the engine feels very smooth and not strugling with the 24's but just cant get the rev's. We have tryed all the usual trimming out ect but still no more rev's or speed.
Engine does not smoke or burn oil starts and ticks over like a dream,
just want that little bit more.
Any help would be greatly recived

Jon Fuller · 08-09-2009, 11:36 AM

Does your exhaust go out through the transom, or through the drive/prop?

scarab racing · 08-09-2009, 12:09 PM

Hi Jon
It goes straight through the transom.
Small amount of black smoke when throttles first opened, until turbo cuts in then no smoke at all, runs and sounds very sweet and smooth
Regards
Mark

Cookee · 08-09-2009, 12:36 PM

Jon and Tony Davis are probably the experts, but if it was an outboard I would get the prop thinned a bit and some pitch taken off it, (Not sure if you can thin props for diesels or whether they would crack from the torque?) the other thing would be to reduce the weight in the boat especially up in the bow - do you have an anchor in the bow with chain? It would be interesting to move it to the stern if you do to see what happens.

Also what do you want? Is it outright speed or do you want to keep the acceleration from a standstill? Everything is a compromise!

Jon Fuller · 08-09-2009, 12:49 PM

Although you've told us the revs, can you give an idea of the speed you're getting, and what this boat weighs?

scarab racing · 08-09-2009, 01:07 PM

Hi Cookee
No weight in the nose, anchor is under passengers seat, batteries are in rear and fuel tank is center mounted under floor, boat sit level and runs very level when under speed,
Have tryed moving weight around, ie passengers siting in the front cabin then moving back to cockpit. Yes does make a difference, better speed when not in the front cabin. ( a couple of mph and a few rev's more but nothing major)
Cant real make a weight saving apart from less fuel, only carry a few basic tools 4 fenders mooring ropes and anchor rope. so not a lot i can throw out.

The engine/boat feels like it can handle the 24" pitch as the acceleration is that good. or should I drop to the 22" more rev's less pitch= More speed?

Am I right in thinking the 22 would give even more acceleration?,
I dont mind if i lost a bit of acceleration to gain on the top speed, I no its a pay off but hay I'm a bloke on "boat mad" I think the answer is going to be TOP SPEED.

scarab racing · 08-09-2009, 01:10 PM

Hi jon
As for weight I realy dont no,(guess 2 -2.5 tons)
As for speed we are showing 32 knots at 3300rpm

Jon Fuller · 08-09-2009, 01:24 PM

mmmn, that's not good!

I'd be looking to ensure the injector pump is seeing, and reacting to the boost (assuming the turbo is ok, and it is starting the boost cycle. In reality I would think it is, as I'd be very surprised if it would do 35mph without any boost)

As the boost comes on, it should act against a diaphram on the pump that raises the fuelling in line with the boost. If that process isn't happening for any reason, I reckon you'd get what you've got.

could be the diaphram, could be the pipe delivering the pressure to the diaphram, or could be a more involved problem in the pump itself, mebbe a stuck part.

Sounds like it's running too clean to me, for the labour it should be under.

dunno what ratio drive you have, but would expect you to need props of circa 26-28" pitch. and probably 55-ish mph

JOSH · 08-09-2009, 01:37 PM

Has your engine ever over heated if so thay crack the ex side of the turbo.
had a sunseeker that did it and fited new turbos and gain revs and speed.

check the boost you are geting with a manual gauge and ex temp as well tells you the loading on your engine and shows your if you are geting full rack.

a quick cheat is to fit a hand pump on the boost compensator on the fuel pump and give it wot and pump the hand pump it give full fuel then full boost is about 32 psi i think. if u start geting black smoke out the back then you are not geting full boost from the turbo.

hope that helps josh

scarab racing · 08-09-2009, 01:41 PM

The turbo is defo spinning up and working as it does give a big kick around the 2500-3000rpm range. i agree the engine is purring and does not sound strained at all and no smoke not even a hint at 3300rpm

As for the speeds that you are saying that is what i would like/love to see.

Is there any test i can do on it whilst on land with pump still on engine to check diaphram or would you surgest a remove and send for testing?.

regards
mark

scarab racing · 08-09-2009, 01:47 PM

Hi josh
I dont have a turbo preasure gauge, but will get one fitted and find out preasure.
I do have an exhaust temp gauge and that never really warms up only just moves of the first setting on the gauge,
The engine has never over heated so we are good thier, and turbo is all intact and spinning free.
Will try your surgestion and let you know.

TECKNO 40 · 08-09-2009, 06:57 PM

How many hours has the engine done? we have had them block the intercooler and build up loads of carbon in the compresser housing wearing away the comp wheel

scarab racing · 08-09-2009, 07:32 PM

engine hours approx 300 max (second hand engine so dont no the full history or hours) very good condition inside and out as engine has only just been fitted so checked and head removed and inspected before it was put in boat.

JOSH · 08-09-2009, 09:34 PM

When thay do crack thay crack across the wast gate port in ex side. Worth a check. Hope you sort it soon
josh

scarab racing · 09-09-2009, 08:10 AM

Hi Josh

Many thanks for the advise will pop down at the weekend and have a look and check out what i can. (will also check diaphram and pipe thank you Jon)

A big thank you to all, for the help and advise.

It has given me some idea's of what and were to look.

Will give an up date as soon as I find anything or get the extra rev's. Hopefully will let you all know soon

Regards
Mark

scarab racing · 25-10-2009, 11:45 PM

Had the boat out today and we have found the problem " a cloged / dirty fuel filter".
Had the 24" pitch props on and we reached max rev's at 4000rpm with great acceleration and top speed of 41 knots (GPS)
Next time out going to up to 26" props and see if we can get a few more knots.
Thanks for all the advice but it came down to a couple of quid filter.
So going to drain tanks and clean out.

Jon Holmes · 26-10-2009, 12:05 AM

Thats good news, keep us updated with the prop testing.