Advice on P28 outboard mounting height / shaft length

[pugracer285]

Hi Guys,

My boat was previously run with 2x Yam 250 4-strokes on which meant that due to their size they were mounted quite far apart. I haven't been able to confirm but assume they were a 25 inch shaft length.

They fabricated a heavy duty transom bracket for the Yams which has support ribs running vertically either side of the engine saddles, it's also effectively raised the top of the transom up by around 2 inches.

It has been suggested that I should mount the current Merc EFIs closer together for better high speed performance / stability.

In order to do this it will require the removal of both engines, removal of the transom plate and then grinding off the horizontal strengthening ribs. In an ideal world I'd have a new bracket made up but too much cost for now.

The current Mercs that I'm running have 25 inch shafts and the cavitation plates are sitting about 2 inches above the transom/hull meeting point. (They don't have low water pickups so I wouldn't want to go higher)

My thinking is that if they come in closer together then they'll also need to be dropped down so that I don't get cooling issues.

In order to drop them, I'd have to completly remove the bracket and put the engines straight onto the transom. (not sure what I'll find under it until we try to get it off)

Going off on another tangent, we are looking at the possibilty of swapping the engines for 225 Optimax in either 20 or 25 inch shafts. I might get away with 20 inch shafts with the Optimax semi low water pickup but probably need to look more at the 25 inch models.

I'd be grateful for any feedback from those who've set these up before as to what they'd suggest.

There are a couple of shots below to try and show what the setup is.

I can take some measurements over the weekend if it helps.

Thanks in advance

James

[Ph@ntastic]

Can't help out , but nice to see the engine's prev. serviced @ Bonestroo Bootmotoren Harderwijk made it to the UK

[driver510]

i would run 20 inch on this with sportmaster boxes if you need info on set up call me on 07702 958175 thanks richard

[Tony Davis]

I'd junk the bracket and go straight onto the transom. I had the bracket off to have some welding done on it, and other than a few bolt holes etc the transom is in pretty good shape.

I think if the motors were closer, it'd go and handle really well.

[Big Dutch]

Don't put them too close together on the transom-you might consider upgrading to Alien cowlings which are wider then the older style one-just a thought !

[CB1]

Chris Lewis always said run pairs at 19''. Just enough room to turn, but by f+++ will it go.

[Burty]

You can squeeze them in at 18" centres but you will have to mod the cowl hold down clips, mine are at 19" centres. think you need 23" centres for aliens

[pugracer285]

Just an update on this....

Firstly thanks to all for the suggestions above.

I am definately going the 225 optimax route on 20in shafts. (one sourced and another ready to buy as soon as my EFIs have sold)

The alloy transom bracket will be removed so that I can go straight onto the transom.

The opti comes with both a side and nosecone water pickup (having read up on it will need to block off a few of the upper side cooling holes) so cooling should be ok.

Sportsmasters would be a nice upgrade but other things to spend the ££ on at the moment.

Will mount them as close together as possible - the Opti cowlings look wider than the EFIs but nowhere near as wide as the previous Yams.

For around $1250 per engine (ex shipping from Simon Motorsports in the US) I can buy lighter flywheels, exhaust tuner, carbon reeds (as optis apparently have a tendancy to eat the std steel ones) and a remapped ecu which should take power to around 280-290hp. Not something I'm going to rush into but nice to know there are upgrades out there for the 3.0L Opti!

Obviously can't do the mods if we end up marathon racing her but my chiropractor is heavily advising against that so perhaps I should just focus on turing her into a weekend speed machine!