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Old 13 April 2012, 19:31   #1
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Country: USA
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Make: Avon 5.4 SR
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Avon 5.4 SR with twin 40's performance?

Hi,

Just bought an Avon SR 5.4 with twin Mariner 40's. One is in need of rebuild. I was considering putting a single E-tec 90 on but am curious about the performance data with the twins.

Does anyone know how this boat performs with twin 40's. The Mariners are light and I like the redundancy but I want the boat to be FAST!

Thanks!
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Old 14 April 2012, 01:44   #2
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Country: UK - England
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If you want the boat to be fast then I would fit the e-tec you will also halve your fuel bill !
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Old 14 April 2012, 03:06   #3
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Make: Atlantic, Searider's
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Hi, I used to have twin yamaha 40's on my 5.4m SR. There are issues with twins. Firstly, doubled the fuel cost to a single fourstroke/etec ( I have a 75hp Merc 4Snow) . Double the service cost etc. Don't get to excited by the possible speed, you will get 31knts top even trimmed up ( the Merc does 35.5kts ). Then you will have serious chime walk issues If you don't put counter balance weight in the front. I had to get nearly 40kg balast grp'd into the front.
I found the perfect balance using sandbags to start with. The twin setup is great for redundancy and loss o steering ( if you have hydraulic baystar or seastar instead of teleflex. You can clamp the ram at the rear and drive back on just engines )
All in all, it's a bit of an effort changing the boat back to a single, because your boat was probably an original fire rescue craft the transom might have some rot problems converting it to a single. Plus if you have the balast in, fitting a fourstroke could work great.
If your worried about lack of power, my 75hp fourstroke is faster than my 80hp yammie 2S and tohatsu 90hp 2S.
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Old 14 April 2012, 05:39   #4
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Thanks,
Were you able to plane on just one of the 40's?
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Old 14 April 2012, 05:41   #5
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Thanks guys,
benjytaylor, the transom appears fine. I havent drilled into it but I have seen no evident signs of compromise. Besides there being 8 mounting holes instead of four are there any other reasons you suspect there may be transom rot on the fire rescue boats?
When you converted did you have to move the drain hole off centerline? And since there is no notch on the transom I figured I might need to go with a 25" shaft. The 2 mariners I have are light, what did your yammies weigh?
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Old 15 April 2012, 12:33   #6
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The yammies are bang on maximum weight for the craft's transom 164kg. Roughly 82kg each, plus the heavy original steel a frame which stresses the transom ( as some people tow of it too ) yes the boat will eventually plane on one engine 13-15knts required to get on the plane.
The hole would need o be moved to the side and the original capped off, of course the 8 holes also need to be capped. Useful if you have a local shipwright to do it for you or tackle it yourself.
The transom will be cut lower to support the twin setup and there is no reason to change that as I have 2 pricing twin seariders ( 1 has been left and one has a brand new transom )

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The blue boat has just been capped and has a long shaft yammie 80hp. The cavitation plate is not exactly spot on to the bottom of the transome but does the job. As you can see the other searider had a whole complete new transom as the old had hidden demons and completely rotten
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Old 15 April 2012, 12:35   #7
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The Merc has also jet ha new toobs fitted this weekend by ribraff :-)
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Old 15 April 2012, 12:49   #8
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Also if you look at the photo of the Merc you will see I had a bowlocker grp'd in with the 40kg grp'd balast at the bottom.

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Old 15 April 2012, 13:21   #9
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Some photo's of the searider with twin yammies before it's refit

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Old 26 April 2012, 11:38   #10
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what is fast ?

I get 31-33 knots @ 5200 rpm with a 90 HP E-Tec on my SR4.7 (15" alu prop).
Inititally i tried a 17" alu prop but it only gave me 4900 rpm wot.
33 knots is fast enough for me on a 4.7m rib...
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