Evinrude 8 hp Yachtwin

[kalo4u]

Just purchased a Yachtwin 8 hp for my sailboat. Haven't ordered a repair manual yet but I have a question that may be answered in the repair manual.
On the (gearcase) extention assembly,number 68,

http://www.boats.net/parts/search/BRP/EVINRUDE/1988/E8SRLCCS 1988/GEARCASE/parts.html

at the base of this case are two square holes that the exhaust utilizes. On the gearcase housing, above the prop, next to the water pick-up is an exhaust plug-item 44,46.

I would like to use the exhaust at the prop area by removing the exhaust plug and sealing the above exhaust ports on the extention assembly.

Question is can this be done?

Why is there an exhaust plug?

Why this design?

Thanks in advance.
Also I have the repair manual on the way and I have had this motor only a few days.
Mahalo

 

[Rick.]

Re: Evinrude 8 hp Yachtwin

Give it a try but do the fix in a way that you can easily put it back to the way it was. I'm guessing here but I think it is set that way to relieve exhaust pressure. Moving the exhaust relief down will cause more back pressure. Best of luck. Rick.

 

[Vic.S]

Re: Evinrude 8 hp Yachtwin

I have the 6 HP version.

A couple of good reasons for the design.

Firstly the trouble with "normal" outboards on sail boats is that in a " bit of a chop" the prop lifts out of the water if mounted normally. You end up with the prop alternately being in the water and thrashing air and you get nowhere! (been there, got the tee-shirt!)
The solution is to fit a long-shaft engine with the prop more deeply immersed but then you have excess back-pressure on the exhaust which may affect the running and may may it difficult to start.

The Yachtwin has the special extension with the square exhaust outlets several inches higher than the normal outlet which overcomes any problems there may may be excess back-pressure .


Secondly because the exhaust outlet is well above the prop the gases are not drawn into the prop when going astern. You therefore get full astern thrust from the prop. The boat will go as fast astern as it will ahead but more importantly a burst of astern power is much more effective in stopping a boat quickly when manoeuvring in confined spaces.

You don't say why you want to plug the special exhaust outlets and open up the one behind the prop but by doing so you will be removing those features of the Yachtwin that make it so much more suitable for a sailing boat than a standard engine of the same shaft length.

I'd strongly suggest that you use the engine in the way in which it is intended to be used and benefit from its design features.

My engine, mounted on a lifting bracket which lowers it so that the exhaust outlets are about 5" below the surface.

 

[Rick.]

Re: Evinrude 8 hp Yachtwin

Well thanks for that VicS. What you said make's more sense than what I said but I thought it was due to exhaust back pressure. I have a 9.9 1990 Evinrude Yahtwin that I have no use for. To be honest I haven't even tried to get it going but ..... some day. Rick.