Minimum hp for SR5.4?

ncp · 02 August 2013, 00:41

I've read all of the threads that say that the Yam 2-stroke 90 is optimum but just came across a 2 stroke 70 with controls for a good price.

I'm helping a friend with a refurb and we've been looking at 90/115 and trying to stay away from 4 strokes [due to weight]. We'll probably block off the flooding hull if that helps significantly with buoyancy.

thx

Nos4r2 · 02 August 2013, 00:55

I seem to remember Ollyit's 5.4 did about 28kts with a 60 on if thats any help.

ncp · 02 August 2013, 01:02

Ok, so possible but wouldn't be good with extra gear, etc. Probably would hurt resale value down the line too.

EDIT:
Measured from transom notch to keel...just under 21 inches (~52-53cm, I'm guessing). If it were left as is, 20 inch "long shaft" would work. My buddy seems to thing that we should raise the transom up so it's straight across. Does that mean a 25 inch shaft then?

Nos4r2 · 02 August 2013, 01:37

It's a standard longshaft. It's only rated for max 90hp by the way.

You can raise the transom, but getting a used XL shaft motor in 90hp might not be very easy.

ncp · 02 August 2013, 01:56

Quote:

Originally Posted by Nos4r2

It's only rated for max 90hp by the way.

If we found one, this wouldn't be the 1st SR5.4 with a 115hp!!!

Nos4r2 · 02 August 2013, 02:02

Quote:

Originally Posted by ncp

If we found one, this wouldn't be the 1st SR5.4 with a 115hp!!!

Agreed, but I wouldn't like your chances of not getting sued if there's an accident-or of your insurers paying out.

The information is easily available (it's online) and if the boat still has it's ID plate, it even says it on it.

In all honesty there's no point overpowering an SR5.4-you'll never ever use the extra power unless it's mirror calm.

ncp · 02 August 2013, 02:19

Quote:

Originally Posted by Nos4r2

The information is easily available (it's online) and if the boat still has it's ID plate, it even says it on it.

I believe you... Though, I didn't find one, it's ex-navy.

I did a lot of googling last night on rib.net and elsewhere and I couldn't come up with any good literature. The best I found was a screenshot of someones phone that said engine weight not to exceed 175kg
http://www.rib.net/forum/attachment....7&d=1345900463

175 kg = 385 lb....this would technically allow for a 366 lbs four-stroke Yamaha 90hp. That seems heavy!

Quote:

Originally Posted by Nos4r2

Agreed
In all honesty there's no point overpowering an SR5.4-you'll never ever use the extra power unless it's mirror calm.

Probably true but right now we're just looking for the right engine at the right price. I found a ~1996 Yamaha 70 with controls for $2100 while I've also found a 1998 Yamaha 90 for $4400. If a 115 were to appear at the right price, it's going on (an almost 15 year old two stroke motor for $4440 is ridiculous!)

Nos4r2 · 02 August 2013, 02:32

Should have said this in the previous post really.

Mine, solo with an 85hp Yam on it and 70 litres of fuel aboard will do 38 knots. It'll probably top 40kts with someone smaller (I'm a fat git) at the helm. It's rare that it's comfortable to go above 28kts for any length of time though..
It's more important if you're setting up an SR5.4 to get the balance right than to stick shedloads of power on it. Sticking on a big heavy 115hp motor and the extra fuel it'll entail is a bit pointless. You won't be able to go any faster unless it's flat calm and it'll be stern heavy.

Nos4r2 · 02 August 2013, 02:37

http://zodiacmilpro.com/wp-content/u...r-range-IT.pdf

Specs are in there. I think they're on here somewhere too.

The Avon specs are max 2x40hp, or 1x90hp. Max weight 175kg.

You need one specced for twins in order to fit them-they don't have the transom cutout.

ncp · 06 August 2013, 00:58

Nos, going the other direction if I couldn't find anything "vintage", i.e. a carbed 2-stroke, what you go for on the new(er) side?

Yamaha F70 117kg
Evinrude Etec 90hp 145kg

I'd throw the Nissan/Tohatsu 90hp (153kg) in there but I would never find one used in the states...

Getting heavier:
Suzuki DF90A 155 kg
Honda 90L 163 kg
Yamaha F90 166kg
Optimax 90 170kg

Would the huge weight savings of the Yamaha F70 make a performance difference?

EDIT:
Found this thread from March of this year.
http://www.rib.net/forum/f8/sr5-4-wi...oke-54025.html
On page 2, Bushrider is estimating 30 knts max with the F70. Can anyone confirm his estimates?

Nos4r2 · 06 August 2013, 02:05

I'd lean towards the Etec on paper, but Davybouy on here has an SR5.4 with a TLDI 90 on and its apparently quite good.

Avoid the opti 90, it's a downtuned 115 and is physically huge as well as heavy.

whisper · 06 August 2013, 02:15

If you can't find a Yamaha 90hp 2 stroke go for a 90 etec, Bushrider just did the round Ireland challenge on his so he's the man when it comes to feedback for a 90 etec set up

ncp · 06 August 2013, 02:17

Quote:

Originally Posted by Nos4r2

Avoid the opti 90, it's a downtuned 115 and is physically huge as well as heavy.

Didn't even include it for that reason.

Made a chart for myself earlier today, attached.

Excluding the 115's, the which have ratio's of .63-.68 hp/kg, the Etec is next at .62 hp/kg and then the Yami F70 at .60hp/kg followed closely by the the Tohatsu/Nissan and the Suzuki. What I never would have guessed is that the Honda 90 is a slightly better hp/kg ratio than the Yami F90!

ncp · 24 January 2014, 21:38

Old thread but still haven't found a decent two-stroke Yami 90 that's not $3,500-$4,500. And they're all ~20 years old!!!

Just found a mid-90's 70hp two-stroke Yami, good compression, etc. - $1,200. Very tempted...

Sorry, had to vent to you guys!!!

olekils · 31 October 2015, 00:32

This might be irrelevant as this thread is old but I went with a Yamaha F70LA on my 5.4 Searider and it's worked out very well for me. I've got a home-built pilothouse on the boat and still get 28+kts flat out with 2 people plus gear on board. For my purposes (cruising) it's great as it's really economical to run and pretty quiet compared to the 2-stroke Merc I replaced.

9D280 · 03 November 2015, 14:35

Would you be willing to Rebuild an engine? There are plenty of dead Yams about, and spares are pretty easy to find (don't ask how I know!

)

Proably a bit academic but waaaay long ago I did my "Sportsboat - rescue endorsement" at a Centre on the Clyde who had an SR5.4 with twin 30s (they also had a small fleet of SR4s with single 30s - the twins o nthe 5.4 were there for spares standardisation etc)... anyhow, during the early days of automixing (1987-ish?) the 5.4 ended up for a while being the only one running premix engines at the centre.... well, you can guess what happened.

I can confirm an SR5.4 will plane 5 (may have been 7 - it was long ago!) up with an offset 30Hp on the transom!

ncp · 03 November 2015, 15:48

Quote:

Originally Posted by 9D280

I can confirm an SR5.4 will plane 5 (may have been 7 - it was long ago!) up with an offset 30Hp on the transom!

That's amazing.

office888 · 03 November 2015, 17:13

This thread is very curious for me as well.

My best research for my 1998 Avon D560 reveals it is based on the Searider 5.4, with no water ballast hull, hull weight of 735 lb, and +1.5" larger tube diameter. It has a max hp rating of 115hp, but in the technical specs, it does not list a maximum engine weight.

For my D560 hull, the tech specs specify:
Minimum 50hp with an approx performance of 30 mph.
Maximum 115hp with an approx performance of 55 mph.

I'm thinking about repowering my D560 with a 2016 Yamaha 115 VMAX SHO 4st. The transom is a little punky, so I'm going to strip it down and rebuild it first.

Tech specs for 1998 below:

Pikey Dave · 03 November 2015, 18:08

Quote:

Originally Posted by office888

This thread is very curious for me as well.

My best research for my 1998 Avon D560 reveals it is based on the Searider 5.4, with no water ballast hull, hull weight of 735 lb, and +1.5" larger tube diameter. It has a max hp rating of 115hp, but in the technical specs, it does not list a maximum engine weight.

For my D560 hull, the tech specs specify:
Minimum 50hp with an approx performance of 30 mph.
Maximum 115hp with an approx performance of 55 mph.

I'm thinking about repowering my D560 with a 2016 Yamaha 115 VMAX SHO 4st. The transom is a little punky, so I'm going to strip it down and rebuild it first.

Tech specs for 1998 below:

It's only since the advent of the lardy 4stroke that weight has become an issue. Before, makers could confidently rate the transoms by HP in the knowledge that whatever engine went on it the weight wouldn't be an issue. Then 4 stroke fever came along & people were sticking 90hp Hondas on the back that weighed as much as a 150hp 2 stroke.

office888 · 03 November 2015, 18:34

Quote:

Originally Posted by Pikey Dave

It's only since the advent of the lardy 4stroke that weight has become an issue. Before, makers could confidently rate the transoms by HP in the knowledge that whatever engine went on it the weight wouldn't be an issue. Then 4 stroke fever came along & people were sticking 90hp Hondas on the back that weighed as much as a 150hp 2 stroke.

Note that there are max transom weights for the Searider, but not the Adventure.

A lot of the transom weight capacity of inflatable boats simply has to do with the tube diameter, tube design, and hull flotation. Hence when Zodiac changed the Futura from pointy to truncated?