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Old 16 September 2010, 19:23   #11
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Originally Posted by Pikey Dave View Post
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.
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Old 16 September 2010, 19:29   #12
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me too
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Old 17 September 2010, 09:19   #13
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Country: Denmark
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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 :-)
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Old 17 September 2010, 10:47   #14
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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.
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Old 17 September 2010, 11:24   #15
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I'd beef up the transom stays and put a good Yamaha 90 Betol 2 strke
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Old 17 September 2010, 13:49   #16
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Quote:
Originally Posted by Rogue Wave View Post
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/
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Old 20 September 2010, 06:04   #17
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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).
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Old 24 September 2010, 19:21   #18
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You might find some answers on here.

http://www.etecownersgroup.com/
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Old 11 October 2010, 08:43   #19
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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 13 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 13 x 15 alu. I went out saturday. I could not check top speed as the sea was a bit too rough. However after 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.
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