SR 4.7 repower

[njensen]

Hi, I'm considering to repower my SR4.7 with a Evinrude E-tec 90 HP (comming from Suzuki DT65 ).


The old engine weighs 113 kg.
The E-tec weighs 145 kg.

I use it for diving, fishing, waterskiing ect.



Any comments, complains or emotional outbursts ?

[HUMBER P4VWL]

flying also?!!

Our 5.4 chine walked with a 90 optimax.

What is the max power the transom will take? Also, weight.

[njensen]

Originally Posted by HUMBER P4VWL

flying also?!!

Our 5.4 chine walked with a 90 optimax.

What is the max power the transom will take? Also, weight.

The 90 Optimax weighs 170 kg. That's a heavy engine !

The SR4.7 is specified for 70 HP and around 130 KG engine. However i'm not so worried about the extra 15 kg, i anyway put 500 kg of people and diving equipment in also (100kg diving-tanks right next to the transsom). That also why the 90 HP would be nice (to get on the plane)

The only issue could be when it's empty going full speed, but i never do that for waterskiing, diving or fishing purposes.


The businesscase for changing engine is not good enough if i only look at the savings on full ect.. I need something more, and since it's currently underpowered for my use, i was thinking to add enough power to avoid comming to that conclusion again.

with a 90 HP E-tec i think the boat would accomodate 4 divers with twin tanks and stage bootles, maybe even a driver. 4 divers with twin tanks can just barely get on the plane with the 65HP. It doesn't leave much flexibility when the waves are rising, or even if some divers are the heavy duty type (+90 kg).

I know the obvious answer would be to buy a bigger boat, but then everything else gets bigger as well. Bigger trailer, garage, car, fuelconsumption, ensurance, and last but not least PRICE......

I understand the point about chine walking, but it only happens if you go high/max speed, right ?

The SR have a quite narrow and steap hull, so i my oppinion it needs relatively large engine not to be underpowered. With enough power the water ballast system would actually be usefull also. At the moment i have closed the hull on my boat.

[HUMBER P4VWL]

with that much weight you won't need the ballast system!

Whilst the engine weight is just over, combined with the power being over as well. Irrespective of what you put by the transom, or what weight you have carried within the boat before, the issue is how strong the transom is and its fixing to the hull and deck.

If you laden the boat up with 4 divers plus gear plus driver, plus fuel, then Nail the throttle to get it up on the plane, think of the forces involved.

There is a chance the engine will just push through the transom and crack it. You will end up having to buy a 5.4 or bigger anyway, but with no decent boat to part ex. 4.7's are like rocking horse poo. (rare) and command a price similar to the plentiful 5.4s. Reason is they fit in a garage, so most urban dwellers can't use the 5.4. I think you could do a great deal selling it and buying a 5.4 then purchasing your etec 90 and have one v nice boat. Specced to its limit.

I'm no engineer but my thoughts are that you are pushing a hull and transom beyond its capabilities. There are more knowledgeable people on here though who will no doubt assist.

[Max...]

I'm no expert but prior to buying my 4.7 SR I spend night after night searching and reading archived topics on all things Searider - IIRC consensus was the weight/power limit is there for a reason. Maybe try a different prop first on your existing engine would be a lot easier/cheaper?

[njensen]

I get your point. Anyway if it was totally obvious for me i would just do it.

The thing is that the SR4.7 and SR5.4 are identical if you disregard the length. The dimensions of the transom and the mounting to the boat are the same.

Ok - i have not disasembled both boats and checked the inside, but i have seen both types in real life. I don't see any difference what so ever. I think the 0.7 meter of extra fibreglass in the front is what justifies the CE marking for 90 HP on the 5.4 meter (longer boat = better stability).


Has anybody in here any exprience on the topics ? (larger / heavier engine than specified)

[njensen]

Originally Posted by Max...

I'm no expert but prior to buying my 4.7 SR I spend night after night searching and reading archived topics on all things Searider - IIRC consensus was the weight/power limit is there for a reason. Maybe try a different prop first on your existing engine would be a lot easier/cheaper?

Hi Max,

actually i did quite a lot of trial and error on the prop side.

16" alu -> too big (top speed 36 knots)
15" alu -> too big
12-16" adjustable Carbon -> ok size, but performance wise it's average

11 1/8 x 14 Stainless -> optimal for my use (topspeed only 32 knots, but very nice ability to accelerate with a lot of weight).

[BlueFlash]

I reckon the E-Tec 90 is a good bet for your boat. The power to weight ratio is very good and if you are using it for diving in cold water one always seems to have lots of weight onboard and the extra oompf is appreciated. I owned 2 of them for 3 years and they gave me good service. Just note that the actual HP output is not really 90HP - its more like 80 to 85HP as the block is the same as the E-Tec 75 just mapped/tuned up a bit. If you do decide to go for it then have a look at the E-Tec owners forum for detail about setting it up with the correct battery/fuel filter/fuel hose/prop as those things make all the difference with getting E-Tecs to perform.

Regards,
Grant

[njensen]

Originally Posted by BlueFlash

I reckon the E-Tec 90 is a good bet for your boat. The power to weight ratio is very good and if you are using it for diving in cold water one always seems to have lots of weight onboard and the extra oompf is appreciated. I owned 2 of them for 3 years and they gave me good service. Just note that the actual HP output is not really 90HP - its more like 80 to 85HP as the block is the same as the E-Tec 75 just mapped/tuned up a bit. If you do decide to go for it then have a look at the E-Tec owners forum for detail about setting it up with the correct battery/fuel filter/fuel hose/prop as those things make all the difference with getting E-Tecs to perform.

Regards,
Grant

you're right... the 4.7 tends to get a bit packed when loading all the gear, that exactly why i'm dreaming about the extra power.
Have anybody measured that it's not giving 90 HP ? I know it's the same engine but different SW or whatever...
In dk the price of the 90 is 26% higher than the 75, i don't know the reason, it's strange. Even the 115 is cheaper than the 90 (-6%)....

[Pikey Dave]

Sell your boat as it is, & buy a bigger one that WILL take all your divers in comfort & put the V4 115 etec on it, a much better engine than the I3 90hp. You will be happier with the end result, i.e. a boat that does what you need it to do & not an overpowered one that doesn't.

[Nos4r2]

Originally Posted by Pikey Dave

Sell your boat as it is, & buy a bigger one that WILL take all your divers in comfort & put the V4 115 etec on it, a much better engine than the I3 90hp. You will be happier with the end result, i.e. a boat that does what you need it to do & not an overpowered one that doesn't.

Exactly what I was thinking.

[Downhilldai]

me too

[njensen]

Thanks guys.. i appreciate your comments.

from a certain point of view i agree with you. Staying below the rated power makes sense. However "solving" my issue by buying a bigger boat is not really a an option for me, even if it technically would be the right thing to do.

Obviously i don't want to do anything that will be dangerrous. Not for me and not for anyone else.

The SR4.7 will chinewalk at 35-36 knot regardless of which engine you put on it. The DT65 weighs only 113 kg, and i saw this problem with my old big prop. Reducing the topspeed solves the problem.

The reasons why i thought about changing the engine are numerous:

noise, fuel consumption, environmental, pull-capability when waterskiing, plane-capability when carrying divers, trolling capability, reliability and because it's nice to get some new gear.

I have absolute no desire to go fast. 35 knots are more than enough for me in the SR4.7. That's why i believe using the E-tec 90 HP with a prop enabling a speed of 36-38 knots (1 person) would make me achieve all the above. It would propably be a rather small prop anabling that "slow" speed, but resulting in a very nice accelaration capability.


Buying a bigger boat requieres a bigger trailer, bigger garage, bigger engine, new instruments, new A-frame and a much bigger wallet ;-) not to mention the more complicated handling for picking up and launching.

No doubt i would swab my SR 4.7 DT65 for a X 6m 115 E-tec anytime if money and space was no obstacles.

i'll post a reply if i do it, and when know how it's working :-)

[Pikey Dave]

In that case the 90 etec is the way to go, you won't find a current clean engine to match it for economy, power:weight, cost of ownership & that loverrly 2 stroke grunt. Have it set up properly & set it to use XD100 & you won't have any smoke or smell. They can vibrate a bit on tickover, but thats the inherent 3 cyl payoff. Try a 4 blade prop, these tend to dig in better & hold the stern steady, it might reduce the chinewalk.

[Rogue Wave]

I'd beef up the transom stays and put a good Yamaha 90 Betol 2 strke

[spartacus]

Originally Posted by Rogue Wave

I'd beef up the transom stays and put a good Yamaha 90 Betol 2 strke

One here if anyone is looking. http://www.outboard-services.com/

[njensen]

i guess it's a bit nerdy, but anyway yesterday me and a friend when out to do some sea-trials.

The idea was to simulate the SR4.7 capabilties with a heavy engine. So we mounted 4x10 kg of lead tubes directly on the transom. 20 kg right on the backside of the transom and 20 kg on top (see pictures). The DT65 weighs 113 kg. The A-frame weighs approx. 12 kg.

The boat has a 1 person jockey seat mounted quite much in front of the boat. 62 liters build fuel tank under the seat.

The wind was strong (14 m/s) but offshore so almost no waves.

The max speed with the 11 1/8 x 14 3-bladed SS prop was 31 knot up wind and 33 knots downwind.

Test 1: upwind, 1 person on the seat, 1 person (80kg) standing behind the seat. Trim 1/5 up.
Result: 31 knots, no chine walking.

Test 2: upwind, 1 person on the seat, 1 person (80kg) sitting on the floor right in front of the engine. Trim 1/5 up.
Result: 31 knots, slightly chine walking (nothing extreme).

Test 3: downwind, 1 person on the seat, 1 person (80kg) standing as far back as possible (holding the A-frame). Trim 1/5 up.
Result: 33 knots, no chine walking.


Conclusion:

Putting an engine of 145kg on the SR4.7 should not change the capabilities drastically. Chine walking will be seen at speeds above 30-35 knots depending on the weight distribution in the boat, the trim, and the aero/hydro dynamics in the specific situation. The boat is not designed to be used at speeds higher than 36 knots and hence should not be used for that. When the water ballast system is closed/empty the tubes does not (barely) touch the water at rest (113 kg + 40 kg + 12 kg = 165kg at the transom).

[The Beard]

You might find some answers on here.

http://www.etecownersgroup.com/

[njensen]

It's done... I put a 2011 E-TEC 90 HP on my SR4.7..

It's great !

yes, it's a very powerfull engine for the size of the boat, but it handles it very well.

My first impression was quite good. It's hard to describe but the boat feels better than before, actually more confortable.

First i went out with the E-TEC dealer. We used a 13½ x 17 alu prop. Very nice hole shot (2 persons). Top speed 36 knots at 4800 rpm. No chine walking when engine was tilted down. It started when tilting too much up.

We changed the prop to a 13½ x 15 alu. I went out saturday. I could not check top speed as the sea was a bit too rough. However after ½ a mile my girlfriend says (and she does not know too much about boats): "It feels much nicer, not so rough, actually it feels like a bigger boat".

20,5 Knots at 3350 rpm, that's a prop slip of 1%.....

Theoretical max speed would be around 34 knots......

It's very responsive on the throttle, hole shot is incredible compared to the old DT65. I think the trick is to be very carefull on the throttle. The DT65 needed a bit of time to accelerate, even giving it full stick. The new rig only need a small input on the stick to get out of there....

Fuelconsumption is nice and low....

20,5 knots at 3350 rpm => 1,6 NM/liter = 0,63 L/NM (trimmed all the way down due to waves)

that's around 60% lower than with the DT65...

In idle it's 0,39 liter/hour... the same as idle in gear at 2,6 knots...


At rest (flooding hull closed) the tubes are barely touching the water, so not much have changed here.

[njensen]

A few upgrades, and it’s still a great boat :-)