Outboard tilt/trim

[Modster74]

Hello all, my first technical question if anyone could offer advice, I've just purchased a second hand yamaha 20 outboard to replace the cheap Chinese one that came with my boat (Mayland 20) how do I know what angle tilt/trim to have it set at? It's my first boat so very naive at the moment, thanks in advance 

[Alan de Enfield]

3 hours ago, Modster74 said:

Hello all, my first technical question if anyone could offer advice, I've just purchased a second hand yamaha 20 outboard to replace the cheap Chinese one that came with my boat (Mayland 20) how do I know what angle tilt/trim to have it set at? It's my first boat so very naive at the moment, thanks in advance 

 

Normally the boat will ride 'bow high' when moving, this means the transom is at an angle to the water. You should adjust the tilt/trim angle so the boat engine leg is vertical when underway.

 

When the leg is at the correct angle the boat should be 'level'.

 

 

[ditchcrawler]

Sounds like try it and see, then adjust if required

[BEngo]

Mang large outboards have a power trim facility so it can be adjusted to suit the speed in use, whilst moving. The goal is to have the propshaft centreline horizontal at all times.

[Alan de Enfield]

13 minutes ago, BEngo said:

Mang large outboards have a power trim facility so it can be adjusted to suit the speed in use, whilst moving. The goal is to have the propshaft centreline horizontal at all times.

 

I cannot think of any 20hp OBs with PTT.

 

Edit :

 

How things change - a quick search shows Tohatsu and Honda have 20hp models with PTT 

Edited May 24 by Alan de Enfield

[Modster74]

Thanks for the replies guys, it's an older motor without ptt, I'll set it at the same as the 10hp one that's on now which seems to work fine and take it from there.... 

[Modster74]

On 24/05/2026 at 19:28, Modster74 said:

Thanks for the replies guys, it's an older motor without ptt, I'll set it at the same as the 10hp one that's on now which seems to work fine and take it from there.... 

Second thoughts With the new motor being 20hp and therefore heavier than the 9.9 that's currently on, maybe I shouldn't set it at the same angle 🤔 

[Alan de Enfield]

It should be set so the leg is vertical in the water, and the prop is horizontal.

 

Don't assume that the 9.9 as ever set up correctly.

 

I take it you knew about the different leg-lengths, and you correctly measured your transom before you bought the 20hp -

 

Very short - short - long -  xlong - xxlong

 

If you have a "long" depth transom and you purchased a "short" length leg you will not get anywhere as the boat is shielding the the prop and stopping it getting any water.

 

The cavitation (anti ventilation) plate must be aligned with the bottom of the boat - It must not be above the bottom of the boat, but, it can be a couple of inches below the bottom of the boat, ideally it should not be anymore.

 

                    

 

18 minutes ago, Modster74 said:

Second thoughts With the new motor being 20hp and therefore heavier than the 9.9 that's currently on, maybe I shouldn't set it at the same angle 🤔 

 

Edited Tuesday at 12:30 by Alan de Enfield

[Modster74]

Thanks Alan, some great advice there, haven't went as far as measuring the transom, but the 9.9 is a short and sits where it should and so is the 20 so should hopefully be fine. 

Now my next task is trying to swap them out in the water 🤣 

[Alan de Enfield]

Tie a rope onto the engine and have a helper keeping some of the weight on the rope - then WHEN it slips, hopefully they can keep the engine out of the water.

 

Dropping the engine into the water is not the 'end' but it is a bit of a job getting it back into a usable condition.

 

When fitting the OB to my tender it slipped and fell off into about 30 feet of water.

Hours of throwing and recovering a grapnel eventually bought it back - it was nowhere near where it went into the water - I think it must have 'fluttered' as it went down.

 

It is then the fun starts :

Drain all the oil out and flush with fresh oil, refill.

Drain all of the fuel out and flush with fresh petrol, refill.

Remove and strip carb(s) reassemble and refit.

Wash down the exterior with fresh clean water.

Dry everything off.

 

Once all reassembled it should start - leave it running for an hour to get hot and get everything dry and flushed thru.

 

EXCEPT when it doesn't start - I pulled on the starter until my arms ached, choke in, choke out, throttle moved to different locations - nothing.

Stripped the carb again and found a "bubble" (micro globule) of water blocking the jet - blew it out, reassembled and it started 1st pull.