OK .. trim or not to trim ....

[Refueler]

I am not a mobo person really ... having been a sailboat person most of my life. Mobo's have been an occasional item apart from the ex soviet speedboat I have.

The Primor 24 has a 170HP VP AQ170a with 280 sterndrive leg ....

She has manual electro-hydraulic trim tabs as you see .. and I have suspicion that the port side one may not be operating as well as the stbd - I noted a slight oil sheen on the water after testing the other day alongside pontoon.

The question is :

Do I use the sterndrive leg trim as well as trim tabs when running ?

I have had conflicting advice on this ... one person said yes to get prop face as near perpendicular to horizontal and get max thrust ... while most have said no as that is only with outboards ... that I should just concentrate on using the trim tabs to get hull to best angle. That using the trim on the drive leg can lead to premature failure of the bellows .. they also advised not to lift leg when boat not in use ... that its really only for beaching / shallow water and trailering ..

So over to you guys and gals ....

 

[ss2016]

I also came from sail and was asking this a year or so ago. I did also talk to the folk who make the tabs. Where I ended up is this.
- Set the leg about right. (Thrust parallel to surface.)
- Adjust the tabs
- Reset the leg
It's iterative. You could keep going but in reality you can't see further speed increases.

I have never heard of the drive angle harming the bellows. Steering is a much greater movement than up/down.
Leaving the leg lifted in the water when the boat is not in use is clearly a bad idea since any deposits on the push rods will damage the seals. On land? I don't but I can't really see a problem. I guess it does leave the bellows distorted into the non-usual relaxed position.

Hopefully someone with more knowledge than I will contribute.

 

[julians]

This is how I look at it

-the outdrive trim can be used to determine the angle of attack of the hull in a range from pointing up in the air to ploughing a small furrow.

-the trim tabs can be used to compensate for a list to port or starboard, and can be used to point the bow even further down than just using outdrive trim, but they can't be used to point the bow up.


So, use both outdrive trim and tabs to achieve the hull angle You want to achieve. There is no one perfect hull angle, you may want to trim for efficiency but then the ride may not be comfortable, or maybe it's not dry, or you may want to trim for comfort but then it may not be an efficient angle etc.

If the sea is calm ish i usually end up with the outboard trimmed up a little to lift the hull more clear of the water to improve efficiency, and have the trim tabs as retracted as possible, this gives the most efficient (as in uses less fuel) running.

But if there's a breeze from port or starboard the boat wants to lean into the wind, so I'd then use one trim tab to counter the lean, but this will affect efficiency a little.

If I'm going into a head sea, then I'll have the outboard trimmed fully down, but the tabs retracted, this makes more use of the pointy bow to cut through the waves without slamming, but is less efficient.

If it's really quite a rough head sea then I'll have the outboard trimmed all the way down, and also I will have both Tim tabs lowered a varying amount to really push the bow down for more cutting ability etc.

Trying to achieve max speed in a flat sea? outboard trimmed out until the boat speed stops increasing, and both tabs retracted to lower the drag as much as possible.

Towing a wakeboarder who wants a big rampy wake? Outdrive trimmed down to plough a big furrow, plus one trim tab extended to push the side of the boat the wakeboarder likes into the water to generate a bigger wake on that side..


So there's no one answer, but do use them all depending on what your trying to achieve.

 

[stelican]

It would be unusual to have a power trim facility on a 280 drive. The trim on a standard 280 drive is adjusted on the tilt pin, from memory there are 4 or 5 positions
The drive has a lifting facility via an eletro /mechanic lift motor and ram which will be forced closed if fwd drive is applied (hope my memory is correct here).
You could also purchase a version of the drive that had external hydraulic trim rams mounted in large housings either side of the sterndrive, Yours does not appear to have these in your photograph.
If yours is the standard drive the best way to set up is to do several runs with the tilt pin in different position until you find the positon that achieves the highest speed, you can then use the trim tabbs to assist the hull onto the plane.and then use the tabbs for leveling port and stb

 

[Refueler]

It would be unusual to have a power trim facility on a 280 drive. The trim on a standard 280 drive is adjusted on the tilt pin, from memory there are 4 or 5 positions
The drive has a lifting facility via an eletro /mechanic lift motor and ram which will be forced closed if fwd drive is applied (hope my memory is correct here).
You could also purchase a version of the drive that had external hydraulic trim rams mounted in large housings either side of the sterndrive, Yours does not appear to have these in your photograph.
If yours is the standard drive the best way to set up is to do several runs with the tilt pin in different position until you find the positon that achieves the highest speed, you can then use the trim tabbs to assist the hull onto the plane.and then use the tabbs for leveling port and stb

This appears to be closest explanation to what I have ... as the to 'pin positions' .. I have not seen - but will have a good look when she's lifted.

Yes there is a electro-mechanical lift motor and was one of the items the nay-sayers mentioned .. saying it was not designed to be run seriously at any angle than down.

'Julians' ... I note that you mention outboard ... as I know - outboards - you can trim either manually by pin / trolling latch / by hydraulic rams .. but what I'm talking about here is a Sterndrive leg - specifically a Volvo 280.

 

[Refueler]

OK ... this confirms only use the pin position to alter the4 drive leg trim ... not the lift motor :

Help on a Volvo penta 280 outdrive with worm gear tilt - BAYLINER OWNERS CLUB

 

[oldgit]

The outdrive 280 with the T & T capability was the 280 T.
The leg was lowered and raised and trimmed by a a pair of hydraulic rams and not the electric motor from the wifes Electrolux vacuum cleaner.
These rams were dual purpose as the they also worked exceptionally well as quick dissolve anodes.
280T was Volvos neat way of testing out a hydraulic tilt and trim system on the unsuspecting public in the dog days of the 280 before introducing the ultra reliable virtually requiring no maintaince or servicing 290 series... with added more up to date grief designed in.

The little alloy castings behind which the almost constantly weeping hydraulic rams lurked , made the most attractive and cosy home for any barnycules within swimming distance on the south eastern coast.
It was of course almost impossible to get in there and clear all of them them out of course.
Many died a painful and lingering death after a thick coat of that stuff in the tiny weeny tin of expensive "special for outdrives goo" was slapped over the top of them.
The little tilt and trim calibration device on the steering hood to let you know what angle the legs were at sometimes worked for whole weeks before giving up.
Please note the little unpainted 1" gap between the transom assembly casting and the hull anti fouling.
This allegedly was to stop any reaction between the aluminium assembly and ones anti foul.

Thank your lucky stars outdrives are so much easier to sort these days.

 

[Refueler]

I have a second question on that leg / motor combo ... what RPM ....

 

[julians]

This appears to be closest explanation to what I have ... as the to 'pin positions' .. I have not seen - but will have a good look when she's lifted.

Yes there is a electro-mechanical lift motor and was one of the items the nay-sayers mentioned .. saying it was not designed to be run seriously at any angle than down.

'Julians' ... I note that you mention outboard ... as I know - outboards - you can trim either manually by pin / trolling latch / by hydraulic rams .. but what I'm talking about here is a Sterndrive leg - specifically a Volvo 280.

Same trimming principles apply to outdrive or outboard, but I didn't realise that your specific outdrive doesn't actually have a power trim, I thought power trim was present on all outdrive, even old ones. I was assuming you had power trim.

In your case you're going to be a bit limited in how much you can adjust things on the fly.

I guess you'll probably have to set it in a mid position and leave it, maybe experiment with positions and find the best compromise. Trim Too high and it could cavitate in turns, and be slow to plane (or possibly not plane at all), and run too bow high. Trim too low and your top speed will be lower, or you might not be efficient etc.

I always found with old outboards that didn't have power trim on small boats, that the second or third hole from fully trimmed in was the best compromise. But I think you're going to have to experiment

 

[Refueler]

I found the books (all in Swedish though) ... the 280 drive - basically a later 270 ... has three pin positions .. the middle one being the norm.

How you actually change the pin position in water ??? The pin is well below waterline.

One job I need to do is identify the Trim Tab system .. its not Bennett as far as I can tell ...

Here's the controller for it :

But I cannot find anywhere that identifies it ..

The pump :

 

[stelican]

AttnJulian
As in my earlier post.

Yes I had alot of experience on finding best trim pin position and as l describe earlier was the best solution.
I did have the benefit of a crane and a slipway!
Refueler
How does the boat run now.
Does it plane easily and run slightly bow up. Does it achieve max revs
If all as above trim pin is in correct position
Boat needs to be out of the water or you need to under the water to adjust trim pin!

 

[Refueler]

How does the boat run now.
Does it plane easily and run slightly bow up. Does it achieve max revs

Yes she seems to get up OK. The revs actually climb at a steady pace .. if you open throttle - she definitely has load on - but revs do peak - in fact too high I suspect as she's hitting 5500 - 5600 if I gun her ... manual says 5000 max.

If all as above trim pin is in correct position
Boat needs to be out of the water or you need to under the water to adjust trim pin!

 

[stelican]

Sounds like it would take a larger pitch prop. But that's not easy to advise on and may involve trial and error.
Volvo Penta used to publish a prop chart. Don't know if still available.

 

[ChromeDome]

The trim does the same on a sterndrive and an outboard - with the difference that outboards can be fitted higher on the transom. Volvo decided where to fit your driveline, so that is a fixed parameter.

Trimming IN (leg closer to the transom) will use engine HP to lift the stern (pushing the bow down). As does pushing trimflaps down.
And vice versa.

Another notable difference is the trimflaps' ability to righten the boat if load is not evenly distributed SB <-> BB. The same goes for side wind when on the plane as wind will push the boat to one side and you'll countersteer to keep the course. A deep (-ish) hull will lean "into the turn" hence tend to list notably when going straight in a side wind. Using one side's trim will help this annoying behavior.

With a fixed trim (pins), you aim "for parallel with the keel line" as a starting point and leave it there until tests have told you how it operates with this and your trimflaps. If good, no need to change.



RPM's at WOT (wide open throttle) with your normal load must reach the specified RPM range as this ensures the engine load is optimal (HP and torque @ RPM). As Volvo states an RPM range, you ideally aim for the high end of range. If not correct, the option is to change the "gear ratio" by changing the propeller pitch. The prop pitch (the distance a prop will travel in theory by turning one full turn) logically decides how fast you go at any given prop shaft RPM - and consequently how much your engine will have to work, to achienve the desired RPM. Limited by the HP on tap as if the engine doesn't reach the RPM with the load, it just hasn't got the nedded HP. Decrease the pitch to increse RPM (and acceleration) - and vice versa.

One inch pitch will change engine RPM by 200 by rule of thumb but as most manufacturers offer pitches in 2" increments, the RPM steps will be +/- 400.

Talking about speed: On a boat like yours the top speed can be calculated on the basis of HP and GW. Let me know your good-to-weight and I'll make a close guess of your top speed. This also indicates, that if lookng for performance the first (and FREE!) task is to remove dead weight from the boat

BTW: Back in the day HP was stated as "on the Flywheel". Later it became the prop shaft to compensate for driveline loss. The true prop shaft output of your good 'ol 3 liter straight 6 might not really be 170.

Did you know that your engine is based on the car engine Volvo created by ading two cylinders to the renown B20, hence calling yours B30?

 

[Refueler]

I am a Volvo car owner of many years ... even my Father was owner of a B10 Amazon .....

Yes the engine is actually the B30 which powered the 164 and its variations.

 

[ChromeDome]

Nice. The longevity of the B16 and B20 was better than the B30.

The B30 was marinized with different heads to solve some of the issues (running too hot on backmost cyl inders)

If you like, a manual for the Volvo AQ170:
Volvo penta AQ170A Manuals

 

[ChromeDome]

Bellows: No problem within trim range, but a very good idea to keep them relaxed (leg down) whenever possible.

 

[Refueler]

Nice. The longevity of the B16 and B20 was better than the B30.

The B30 was marinized with different heads to solve some of the issues (running too hot on backmost cyl inders)

If you like, a manual for the Volvo AQ170:
Volvo penta AQ170A Manuals

I have already .... in Swedish and English !

If you want to talk longevity of engines .... the Volvo 5 cylinder evolution of the Audi 5E engine is in another league ...

 

[ChromeDome]

Yes. And adopted by Ford when they owned Volvo..