Sterndrive Performance questions

[Fire99]

Hi all,

Firstly happy christmas to everyone. Hope all have had a good time with family and/or friends..

As many of you will know i recently acquired a Shetland Black Prince 23 with a Volvo Aq200d 5.0 v8 Sterndrive (200hp) running through a Volvo 280 leg. I've trawled through the search pages but cant quite find the answer to my question so apologies if this is covering old ground.

The boat was quoted at the broker as max speed 30knots with cruising of 20. My first sea run the other day on very calm waters was only around 20 max.
I have to admit im quite new to sterndrives and she has hydraulic trim tabs which are quite eye opening...

My 280 leg has a toggle to bring the leg down and a single amber light which goes out once the leg is fully extended. Am i right in saying this leg has no 'power-trim'? All speed runs were with the leg fully down.
I'm not certain where the trim tabs were during the runs but i know with the tabs fully up the boat would not plane and merely seeked the sky.
Im obviously going to do a few more runs over the next few days but thought i'd ask for you guys for some good starter pointers before i go through lots of trial and error.
And lets face it.. knowledge and understanding is power with these things.

the hull is very clean so there should not be an major drag issues and the runs were with 2 adults on board including me.

After looking at the Performance data from owners on the Shetland owners site, it seems she should be running much better performance.

Both engine and leg were recently extensively serviced before taking collection and the engine runs very sweetly.

As every any advice is greatly appreciated.

many thanks,

Nick

 

[oldgit]

Hi Nick.Your top speed problems,are you using GPS or one of those water pressure speedo thingies.?As you can read elsewhere on the forum top speed is always a very moveable feast with such factors as clean hull and number of people on board making sometimes dramatic differences to speed attained,even wave height will lower speed.On much bigger boats than yours,an few too many crew,full water or fuel tanks will slow you down quite a bit.
Only the "T" version of the 280 legs had a proper trim facility,would guess that the leg in the fully down position would be prob roughly the right location for max speed.If the bow is pushed to far down in the water the results are dramatic and very obvious with the boat veering all over the shop and very difficult to keep a straight heading.Remove every thing movable from boat(except you)try with tanks only half full and test again.

 

[Double arvor]

hi
follow the above also move your trim tabs, was you planning
at 20 knts you will also loose a few knts over the years

 

[Fire99]

Thanks Fred for the reply...
I'm using the Garmin GPS to show speed which i guess is the most accurate measurement...
I have to admit after running twin diesels on shaft, a single outdrive with Trim tabs is certainly a different 'science' though fortunately 4 times faster..
I'll run her up later minus the 3-piece suite and drinks trolley /forums/images/graemlins/smile.gif and have another go...
I was very surprised what a dramatic effect a very subtle change on the trim tabs could make. At one point after attempting to correct a slight lean the horizon took on a slightly unsettling 45 degree angle appearance..

I'll let you know how i get on. many thanks.

 

[Fire99]

i think i'd be defying the laws of physics if i wasnt planing at 20kts. /forums/images/graemlins/smile.gif
But yeah i need a bit of practice with the trim tabs as they have a dramatic affect with quite subtle changes..

 

[Double arvor]

nick
have you got a rev counter, my old shetland 2+2 would do
between 18 and 25 knts dependent on tide , wind

 

[ari]

I'd have thought that a Shetland 23 with a 5.0 litre V8 ought to absolutely fly! I'd expect 30 knots and I'd expect it to plane without needing tabs down rather than just pointing at the sky.

You are right in saying your 280 leg has no power trim, just an electric lift for cranking up the drive when the boat is stopped.

Is the boat weedy underneath? That will make a huge difference to performance.

What revs are you getting?

I'm thinking either she's very weedy, or she's massively overpropped, or you're down on power somewhat.

 

[brianrunyard]

Are you getting between 4,000 and 4,400 rpm at WOT?

 

[mont]

Merry Christmas to the costa del solent forumites from humberside.

I am a fan of sterndrives, learnt on them (thanks clive) bought a boat with them, and wouldnt have anything else (apart from ips).

mbm and mby have run some good articles on this subject and perhaps some proper piccies will help you fully grasp the subject.

'One to one' tuition with an experienced sterndrive skipper or instructor may also pay great dividends.

After shafts the very lively performance and speeds will be a little too exciting perhaps at first.

I usually adjust trim by getting someone to shuffle around. Great for delicate trim adjustment and doesn't loose any speed.

Good luck

 

[duncan]

[ QUOTE ]
I'm not certain where the trim tabs were during the runs but i know with the tabs fully up the boat would not plane and merely seeked the sky.


[/ QUOTE ]

having the tabs at all down at full throttle on such a boat will cost a lot of knots - tabs down, throttle on, then as the boat goes through about 15knots wind the tabs up - assuming calm water etc

not being able to trim the drive out at higher speeds will also cost available knots

 

[Fire99]

Hi All,

Thanks for all your replies so far...
Obviously this sterndrive setup with trim tabs etc is a learning curve having owned twin screw on shafts and outboard equipped boats in the past.

Unfortunately the weather today was a touch too foggy on the less than sunny east coast to attempt any high speed runs so today was spent doing some slow speed work and having a bit of practice mooring single-handed at the marina..
As per norm people appear from no-where to watch when you are practicing these things /forums/images/graemlins/smile.gif

Hopefully i'll be able to give the boat some faster runs over the next couple of days and i'll reply back to all the tips and questions so far..
cutting back on the mince-pies may be the first course of action.. /forums/images/graemlins/smile.gif

thanks all and hope your boxing day has been a good one.

Nick

 

[overdrawn]

HI There.
I have a fletcher 238 with twin 3.0lmercs, so its quite a stern heavy boat with total of 260hp.

Try leg in with quite a lot of tab,yes i know tabs cause drag but!! if you can get the boat running flat with the stern less immersed you will go faster,once you are running flat,try trimming the leg out slowly which may give you a tad more speed although it may make the boat a little twitchy.

It all depends on wind/tide/waves and boat.
Have fun
H

 

[ari]

He has a 280 leg with no power trim... /forums/images/graemlins/crazy.gif

 

[overdrawn]

OOOPS /forums/images/graemlins/blush.gif
Tab advice still valid tho /forums/images/graemlins/grin.gif

 

[ari]

Agree, but a little Shetland with a stonking great V8 shouldn't need tabs to get onto the plane.

Years ago I ran a Fjord 21 with a 4 cyl Volvo (AQ171, 167hp) and that'd get up and plane with no difficulty without needing tabs. I'd expect the Shetland to be lighter (it's slightly longer but narrower and I'm sure lighter) with a V8, and I'd expect it to do much more than 20 knots (the old Fjord would nudge 30 WOT).

Reading the initial post I'd guess that either the boat is extremely weedy underneath, or it's significently down on power.

 

[Fire99]

Hi there...

Well i've still not managed to get out and do any further tests.
However, i spoke a marine engineer and he told me the shetland black prince was very heavy for its size. Apparently shetland were very generous with the GRP layup and the cast iron V8 is a heavy lump too.
However i've not substanciated any of that yet..

the engine runs sweet enough.. Very quiet for such an old ohv V8 and compression is good on all cylinders. The engine and outdrive have had a recent service by marine engineers.
The hull isn't weedy as far as im aware since the hull was cleaned shortly before i bought her.
I have downloaded the engine / outdrive manual from Volvo and it states maximum revs at around 4400 with max cruising around 500 rpm lower. that i will check on my next run.

The trim pitch of the 280 leg appears to be set by a pin and has 3 settings so i'd be interested what setting it is on.

Also prop pitch im sure makes a big difference.

Apart from dodgy compression, blocked air filters and poorly adjusted carb etc which should all be ok, i cant think how the engine could be low on power..

Second hand boats can be one serious 'voyage' of discovery.. so to speak

 

[overdrawn]

Absoloutly right,it should leap onto the plane anyway,with tabs used to adjust trim and lean. Could be that the fixed pin is too far out. It is certainly the case that i should have read the first post properly before opening my big mouth /forums/images/graemlins/blush.gif