Mariner 50 hp on SR4 advice

sarran · 02 March 2018, 11:16

Hi everyone, first post here and first RIB too.

I've just purchased an Avon SR4 with an ex RNLI Mariner 50, I initially thought that this would be a great set up but I've come to the conclusion that this is actually a short shaft engine.

https://imgur.com/a/YB9zb

Looks to me like the cavitation is and inch or two too high.

Looking for some advice on if I'm correct and is it even worth trying to use this engine or should I start looking for a long shaft?

jeffstevens763@g · 02 March 2018, 12:03

Quote:

Originally Posted by sarran

Hi everyone, first post here and first RIB too.

I've just purchased an Avon SR4 with an ex RNLI Mariner 50, I initially thought that this would be a great set up but I've come to the conclusion that this is actually a short shaft engine.

https://imgur.com/a/YB9zb

Looks to me like the cavitation is and inch or two too high.

Looking for some advice on if I'm correct and is it even worth trying to use this engine or should I start looking for a long shaft?

yep defo short shaft if its resting on top of the transom

sarran · 02 March 2018, 12:22

Yea don't think it'll sit any lower on the transom, any advice on actually using this engine or is it not even worth trying?

jeffstevens763@g · 02 March 2018, 12:37

Quote:

Originally Posted by sarran

Yea don't think it'll sit any lower on the transom, any advice on actually using this engine or is it not even worth trying?

it will cavitate badly and not perform as it should you need a long shaft bud sorry worth ebaying it and see what's around long shaft wise

Ribtecer · 02 March 2018, 13:03

I've got a mariner 60hp Long Shaft that would be perfect on that.

Trouble is I'm/it's in Hampshire.

PM me if interested. I haven't started advertising it yet.

sarran · 02 March 2018, 13:12

Thanks for the offer, think I'll try and find something local first but I'll keep you in mind.

Ribtecer · 02 March 2018, 13:19

Understood, shame as it's worth considering

samt · 03 March 2018, 06:34

RNLI ran special legs that were 17.5", inbetween short and longshaft. You can see the extension here:

And also attached are the longshaft and shortshaft version of the same engine: (they are tohatsu based engines with Mariner decals).

EP Barrus did the modifications for the RNLI, so a possibility is to buy another leg extention, a long driveshaft, a long water pickup pipe and a long gear shift shaft.

This will give you a longshaft (20") which is what the searider is designed for. I wouldnt cut the transom as the sr4 sits low in the water. They definately flood with a 5" cut out for a shortshaft, a 2.5" cut out wouldnt be much better.

Andy JC · 03 March 2018, 06:53

Quote:

Originally Posted by Ribtecer

I've got a mariner 60hp Long Shaft that would be perfect on that.

Trouble is I'm/it's in Hampshire.

PM me if interested. I haven't started advertising it yet.

Someone correct me if I'm wrong but, I think the max HP for an SR4 is 50.

Nos4r2 · 03 March 2018, 12:04

Quote:

Originally Posted by samt

RNLI ran special legs that were 17.5", inbetween short and longshaft. You can see the extension here:

And also attached are the longshaft and shortshaft version of the same engine: (they are tohatsu based engines with Mariner decals).

EP Barrus did the modifications for the RNLI, so a possibility is to buy another leg extention, a long driveshaft, a long water pickup pipe and a long gear shift shaft.

This will give you a longshaft (20") which is what the searider is designed for. I wouldnt cut the transom as the sr4 sits low in the water. They definately flood with a 5" cut out for a shortshaft, a 2.5" cut out wouldnt be much better.

And will cost more than the motor is worth.

beamishken · 03 March 2018, 12:34

Quote:

Originally Posted by Nos4r2

And will cost more than the motor is worth.

Definately not a cheap fix to convert (even if you can get it apart)
If it is a mid shaft you can often run 1"to 1.5" high in which case you might get away with just trimming an inch off the top of the transom which wouldn't make a great deal of difference you may need to run a prop suited to running high.
I run my 3.8m rib with a 40 yam 1.5"high without any issues

boater · 03 March 2018, 16:30

Quote:

Originally Posted by sarran

Hi everyone, first post here and first RIB too.

I've just purchased an Avon SR4 with an ex RNLI Mariner 50, I initially thought that this would be a great set up but I've come to the conclusion that this is actually a short shaft engine.

https://imgur.com/a/YB9zb

Looks to me like the cavitation is and inch or two too high.

Looking for some advice on if I'm correct and is it even worth trying to use this engine or should I start looking for a long shaft?

How about using a manual jack plate , set at the height you need , boat would have a good centre of gravity too , was thinking of using one on mine

sarran · 03 March 2018, 19:58

Thanks for the ideas.

If I could find the parts to do a conversion that'd be great but I can't seem to find anything available. It's be really good to be able to keep this engine, seems like it's be a really good match for the SR4.

Don't think I'll touch the transom, I'd rather keep it as it was made.

Could anyone provide a like to a suitibe back plate? I'll look into it a bit more and see if it's been done before.

I'll try and get the boat in the water next week for a trial, I'm not expecting much performance but it'll be interesting to find out how much difference it makes when I've got the shaft length sorted.

samt · 03 March 2018, 21:53

Quote:

Originally Posted by sarran

Thanks for the ideas.

If I could find the parts to do a conversion that'd be great but I can't seem to find anything available. It's be really good to be able to keep this engine, seems like it's be a really good match for the SR4.

Don't think I'll touch the transom, I'd rather keep it as it was made.

Could anyone provide a like to a suitibe back plate? I'll look into it a bit more and see if it's been done before.

I'll try and get the boat in the water next week for a trial, I'm not expecting much performance but it'll be interesting to find out how much difference it makes when I've got the shaft length sorted.

Any good Mercury/Mariner or Tohatsu dealer can get the bits, I checked the parts catalogue and your looking at about £550 for the parts.

Its not a difficult job for an outboard mechanic to do. When these engines came out of service, a lot were converted to longshaft & electric start and sold on.

Have a search for outboard jack plate. Never seen one on a searider before. They are normally used for raising the engine. You will have problems with routing your steering cable and controls if you use one to lower the engine.

Unfortunately your 17.5" engine won't fetch as much money as a longshaft version of the same spec.

See how yours runs, its normal to run with the cav plate an inch above the keel. High performance boats often run much higher. But you'll probably find the prop looses grip in tight turns.

beamishken · 04 March 2018, 20:52

Quote:

Originally Posted by samt

Any good Mercury/Mariner or Tohatsu dealer can get the bits, I checked the parts catalogue and your looking at about £550 for the parts.

Its not a difficult job for an outboard mechanic to do. When these engines came out of service, a lot were converted to longshaft & electric start and sold on.

Have a search for outboard jack plate. Never seen one on a searider before. They are normally used for raising the engine. You will have problems with routing your steering cable and controls if you use one to lower the engine.

Unfortunately your 17.5" engine won't fetch as much money as a longshaft version of the same spec.

See how yours runs, its normal to run with the cav plate an inch above the keel. High performance boats often run much higher. But you'll probably find the prop looses grip in tight turns.

So £550 for bits plus £250 -£300 in labour Doesn't make economic sense that's probably what the engine is worth.
I guess it depends how old and valuable the boat is but the only economic way to fit that engine to your boat may be to trim the transom slightly.
If it's a recent boat then it's probably going to devalue the boat too much but if its an old cheapie then probably worth a go.
An inch or inch and a half won't make a huge difference if you just trim where the engine sits

sarran · 21 March 2018, 22:04

So I've finally been out for a trial run and everything seems to work fairly well, it's not very good at sharp turns but I can live with that for now anyway. I wasn't able to get a sped reading but it seems pretty nippy in a straight line.

I'm now looking to do a service on the engine before taking it out again and I'm wondering if anyone can help me identify the parts I need, I believe it'll be the same service parts as a Tohatsu 50D?

If someone could confirm that or even better a link to the parts I need? I've already changed the plugs and given it a general tidy up so I'm looking to do the impeller and gearbox oil now.

spartacus · 21 March 2018, 23:52

Mariner 50hp long-shaft here. Says 'awaiting repair' and I'm sure they've had it for ages.
http://www.seamarknunn.co.uk/download/usedob/used.pdf