Honda 2.3 air-cooled, shaft confusion

mick

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I have a Suzuki 2.5 short shaft which I am replacing with a Honda 2.3 air-cooled. My tender is a round-tailed inflatable with an outboard bracket, which gives a transom height of 45/46cm. This is clearly more than you would get with a fixed, solid transom. The Honda short shaft would place the anti-cavitation plate just above the water surface (empty dinghy) or just below it (loaded dinghy). The manual suggests this plate should be at least 15cm below the water surface. The Suzuki short shaft was OK although the exhaust spluttered if the dinghy was empty (it has other failings). Do I need a long shaft model?
 

VicS

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I have a Suzuki 2.5 short shaft which I am replacing with a Honda 2.3 air-cooled. My tender is a round-tailed inflatable with an outboard bracket, which gives a transom height of 45/46cm. This is clearly more than you would get with a fixed, solid transom. The Honda short shaft would place the anti-cavitation plate just above the water surface (empty dinghy) or just below it (loaded dinghy). The manual suggests this plate should be at least 15cm below the water surface. The Suzuki short shaft was OK although the exhaust spluttered if the dinghy was empty (it has other failings). Do I need a long shaft model?
You have the answer there Your transom height is more than that specified for the short shaft Honda

You need a a longshaft model or you need to alter the transom bracket.. with a lower mounting pad for the engine so that you meet the requirements set out in the owners manual.

Comparison with a Redcrest is irrelevant .......( The extra short shaft, 330mm, Seagull Featherweight was the ideal shaft length for them )
 

Plum

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I have a Suzuki 2.5 short shaft which I am replacing with a Honda 2.3 air-cooled. My tender is a round-tailed inflatable with an outboard bracket, which gives a transom height of 45/46cm. This is clearly more than you would get with a fixed, solid transom. The Honda short shaft would place the anti-cavitation plate just above the water surface (empty dinghy) or just below it (loaded dinghy). The manual suggests this plate should be at least 15cm below the water surface. The Suzuki short shaft was OK although the exhaust spluttered if the dinghy was empty (it has other failings). Do I need a long shaft model?

Suzuki specify a transom height of 381mm and Honda specify 418mm so the Honda has a longer leg than your Suzuki which you said was OK. If i have got the correct specs than you will be ok.

Www.solocoastalsailing.co.uk
 

QBhoy

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Hi. You defo want a short shaft for this tender.
Ideally it’s not about where the cavitation plate is relative to the water. It’s more crucial that the cavitation plate aligns with the line of the hull at the transom. More so on a planing hull.
Inflatables are a bit of an exception to the rule on occasion. Depending on the type, they react differently. Cheaper ones without a keel of any type tend to gulp air under the hull and cause slight cavitation at the prop, when on the plane. So I wouldn’t worry too mich about the cavitation or ventilation plate being a little deeper. That said. A long shaft is too deep. They have a horribly inefficient effect on a small inflatable and often under perform and throw water everywhere.
 

mick

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You have the answer there Your transom height is more than that specified for the short shaft Honda

You need a a longshaft model or you need to alter the transom bracket.. with a lower mounting pad for the engine so that you meet the requirements set out in the owners

Comparison with a Redcrest is irrelevant .......( The extra short shaft, 330mm, Seagull Featherweight was the ideal shaft length for them )


Vic, thanks for that. I’ll have a look at cutting a bit off the bracket pad. If I’m having serious problems with the short shaft I’ll get an extension kit from Steve66.
 
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mick

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Hi. You defo want a short shaft for this tender.
Ideally it’s not about where the cavitation plate is relative to the water. It’s more crucial that the cavitation plate aligns with the line of the hull at the transom. More so on a planing hull.
Inflatables are a bit of an exception to the rule on occasion. Depending on the type, they react differently. Cheaper ones without a keel of any type tend to gulp air under the hull and cause slight cavitation at the prop, when on the plane. So I wouldn’t worry too mich about the cavitation or ventilation plate being a little deeper. That said. A long shaft is too deep. They have a horribly inefficient effect on a small inflatable and often under perform and throw water everywhere.


I do have the feeling that a long shaft would be wrong here, especially as the Suzuki 2.5 was OK. I have never seen a long shaft on a light 8 ft. Inflatable. I appreciate what VicS says (I always appreciate what VicS says) but as I say elsewhere I can always get an extension kit from Steve66.

Anyway, thanks for all replies.
 

quatin

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I sell Honda 2.3 longshaft conversion kit if you do find problems with your short shaft

Sorry to ressurect an old thread, but I have a BF2.3 long shaft that I would like to convert to short shaft. Do you have a kit? Is the work easy? Just remove the extension piece and replace with short drive shaft?
 

jamie N

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I've only done the reverse by making mine longer, and it was as easy as that: a new shaft that simply slotted into place, and the 2 bolts on the extension piece, shortening should be as simple.
The extension piece that you remove does have an ebay value as well!
 

quatin

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I've only done the reverse by making mine longer, and it was as easy as that: a new shaft that simply slotted into place, and the 2 bolts on the extension piece, shortening should be as simple.
The extension piece that you remove does have an ebay value as well!

Well that's great to hear. Sounds like a little summer project for me. Did you have a service manual to follow?
 

jamie N

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Nope, it was really very simple in fact. My motor was already a long shaft, and I'd bought the 'extender' piece, so all I really needed was the shaft lengthening. The 'extender' piece that I'd bought came with a shaft that was the same length as the one already in the motor, so all I did was to take the old shaft, and the new shaft along with the 'extender' section to a machine shop and explain what I wanted to do, which was basically to lengthen a shaft by the 6" of the 'extender' piece.
A couple of days later it was done at a reasonable price.
1665500778438.png
For you I'd reckon that either having the existing shaft modified or purchasing a short shaft (better option), will take minutes of your time.
Good luck!
Edit: I took both shafts to the engineer as it was always the intention to keep one unaltered in case the 'bright idea' didn't work.
 
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Steve65

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Nope, it was really very simple in fact. My motor was already a long shaft, and I'd bought the 'extender' piece, so all I really needed was the shaft lengthening. The 'extender' piece that I'd bought came with a shaft that was the same length as the one already in the motor, so all I did was to take the old shaft, and the new shaft along with the 'extender' section to a machine shop and explain what I wanted to do, which was basically to lengthen a shaft by the 6" of the 'extender' piece.
A couple of days later it was done at a reasonable price.
View attachment 144322
For you I'd reckon that either having the existing shaft modified or purchasing a short shaft (better option), will take minutes of your time.
Good luck!
Great bit of engineering . I machine new splined ends onto honda driveshafts, I.know how precise it has to be or they vibrate like hell!!
 

quatin

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Nope, it was really very simple in fact. My motor was already a long shaft, and I'd bought the 'extender' piece, so all I really needed was the shaft lengthening. The 'extender' piece that I'd bought came with a shaft that was the same length as the one already in the motor, so all I did was to take the old shaft, and the new shaft along with the 'extender' section to a machine shop and explain what I wanted to do, which was basically to lengthen a shaft by the 6" of the 'extender' piece.
A couple of days later it was done at a reasonable price.
View attachment 144322
For you I'd reckon that either having the existing shaft modified or purchasing a short shaft (better option), will take minutes of your time.
Good luck!
Edit: I took both shafts to the engineer as it was always the intention to keep one unaltered in case the 'bright idea' didn't work.
Starting the project a little early. Did you disassemble the lower unit to get just the shaft out? How does the clamp work to hold the shaft in place? I found a service manual, but it's just a blow up diagram of pieces.
 

jamie N

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The 2 bolts that attach the prop gearbox to the shaft were removed, and the units simply separated. The shaft wasn't constrained at either the upper or lower ends, and 'slots' in & out of either end IIRC.
It required no engineering skill in either disassembly or re-assembly, just a spanner really, however as you'd know, getting the elongated shaft perfect is critical, and way beyond my skills level!
 
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