Avon SR4.7 recommended power

michael78 · 15 March 2022, 12:00

Cheers everyone, I am Mike from Greece and I am about to upgrade from an SR4.0 to an SR4.7, will my Honda Bf50 be enough? I have a relatively light setup in mind, center console with no more than 2 persons and their fishing gear. Anyone out there with the same boat/HP to help me?

Limecc · 15 March 2022, 12:10

I think it could work well. The next class up gains a fourth cylinder and is much heavier. I get 29kn from my 4.6m/50hp lightly loaded and underpropped, and a little more when I get to try the new 15" prop. It only goes as well as it does because I took some time to get the engine height right. I was disappointed before, amazing the difference 2 holes higher made.

Conversely I had a well set up 4.2m/30hp RIB before the current boat and was disappointed upgrading it to 40hp because they set the new engine too low. I'd give the BF50 a try before you commit to any upgrade.

P.s. My Suzuki with 15" pitch is equivalent to your Honda with 14" pitch because of different gear ratio.

michael78 · 15 March 2022, 21:22

Quote:

Originally Posted by Limecc

I think it could work well. The next class up gains a fourth cylinder and is much heavier. I get 29kn from my 4.6m/50hp lightly loaded and underpropped, and a little more when I get to try the new 15" prop. It only goes as well as it does because I took some time to get the engine height right. I was disappointed before, amazing the difference 2 holes higher made.

Conversely I had a well set up 4.2m/30hp RIB before the current boat and was disappointed upgrading it to 40hp because they set the new engine too low. I'd give the BF50 a try before you commit to any upgrade.

P.s. My Suzuki with 15" pitch is equivalent to your Honda with 14" pitch because of different gear ratio.

I guess it's worth a shot, my current pitch is only 13" so I will start from there

Limecc · 15 March 2022, 22:10

Quote:

Originally Posted by michael78

I guess it's worth a shot, my current pitch is only 13" so I will start from there

That prop's good for 27kn if you are lightly loaded enough for it to reach the rev limiter.

Nos4r2 · 16 March 2022, 01:42

Stick the max rating on a 4.7 if you can-it's a lot heavier boat than an SR4.

jonp · 16 March 2022, 03:45

Yes it will push it along ok when propped correctly but like the others have said, won't be overly fast but certainly quick enough for most sea conditions. We've got a merc 60 4 stroke on a zodiac 500 pro which is quicker then my 14ft centre console that has a 90 Honda and faster than my zodiac pro tour 550 with a yam f70. The little 60hp merc has had 5 adults and all their spearing weights etc and still managed 29kts in less than good sea conditions.

Limecc · 16 March 2022, 03:47

Quote:

Originally Posted by Nos4r2

Stick the max rating on a 4.7 if you can-it's a lot heavier boat than an SR4.

Yep it can take max 70hp and the boat weighs 250kg.
Mine's heavier at 300kg and of course if I were powering it for the first time 70hp is what it would get. Unless I buy new it's never going to happen, it's hard to source something second hand in keeping with a boat of that age, also I wouldn't want a thirsty two stroke.

And a four stroke 70 is a lot heavier than the two stroke it was designed for. Only the Yam 70 is light enough to be in spec on mine, don't know about the Avon.

jonp · 16 March 2022, 04:07

Quote:

Originally Posted by Limecc

Yep it can take max 70hp and the boat weighs 250kg.
Mine's 300kg and of course if I were powering it for the first time 70hp is what it would get. Unless I buy new it's never going to happen, it's hard to source something second hand in keeping with a boat of that age, also I wouldn't want a thirsty two stroke.

And a four stroke 70 is a lot heavier than the two stroke it was designed for. Only the Yam 70 is light enough to be in spec on mine, don't know about the Avon.

Ive had three of the Yam f70 engines on different boats and all have been fantastic little engines. Over here in Australia they are great value especially if you are clocking big engine hours. I put just under 1000hrs on one in 12months and have been on boats that at the time were over 7000hrs without any problems (tour boats that run 7 days per week doing crocodile watching tours). The Yamaha mechanic I use does servicing at my home and charges around $160-$200 which is 80-100 quid Pommy money!!!

Ive had three Suzuki 4 strokes also which are more costly in servicing as they go through anodes and plugs etc more quickly. Ive also had gearbox issues and electrical problems with my Suzuki engines.

Limecc · 16 March 2022, 04:18

Great info Jon. And thanks for the tip about the Hustler.

69cmw · 16 March 2022, 13:12

I’ve had a SR 4.7 with a 75HP Yam 2 stroke, I definitely wouldn’t have had a 50HP on it, would be pretty gutless [emoji107]

Limecc · 16 March 2022, 13:29

Quote:

Originally Posted by 69cmw

I’ve had a SR 4.7 with a 75HP Yam 2 stroke, I definitely wouldn’t have had a 50HP on it, would be pretty gutless [emoji107]

What prop were you running it with?

69cmw · 16 March 2022, 19:31

Quote:

Originally Posted by Limecc

What prop were you running it with?

Can’t honestly remember as it was 9 years ago, I do know it was stainless though.

J.W.W. · 13 April 2022, 09:28

Run a Mercury F60 on my SR4.7. Perfectly happy with the set

.
Around 36kn single pers. with 16p 3blade.
33kn with 2pers 15p 3 blade.

The Yamaha F70 is a perfect engine too!
Running that at the local lifeguard station on a Ribcraft 4.8.
But tops about similar to the SR4.7 Avon with only F60 Merc.