Wrong Prop

toby4594 · 22 August 2006, 17:55

Couldn,t wait any longer to try out the new prop ,and after seeing the dismal forecast for the week decided that i would take the day off Tues ,as it seemed the best day .
I was told by steel developments when i enquired about this particular prop to expect a drop of 400 rpm this i thought would be ok as engine revs a shade to high anyway.So carrying normal load of fuel and bodies and the great conditions off we went.Our passage through Chichester harbour seemed to take forever but eventually was able to put the hammer down so I did ,and I waited and waited and eventually she dragged herself up to the dizzy speed of 31.5 knts at 5000rpm wot . Ive lost 1000rpm and 8 bloody knts the only plus side to this miserable affair that it does hold it in the turn a lot better .So will call steel devs in the morning and see what we can do .

Cypman · 22 August 2006, 18:16

Sorry to hear it did not work. I have a DF140 with a standard aly prop of 21 ins pitch. Its WOT is 6000rpm which is mid way between the recommended 5600-6300 max rpm. As my boat is used primarily for cruising and I didn't need maximum acceleration I ordered a 22 in pitch S/S prop from Suzuki, unfortunately it also "failed" so I am looking to try the 20 in one.
I believe you need to swap the 23 in prop for a 21 in one and see what happens. Realistically, a 2 in change should give you about 500rpm difference. However, props have a mind of their own!!! Trial and error seems to be the best alternative, good luck

Ribshop · 23 August 2006, 07:37

Funny you lot seem to be having similar problems to what we have experienced with the Suzuki’s.
We rigged some 140s on 6.5m’s, the props supplied by Suzuki were absolutely useless! Cavitation was the worst I have ever experienced! After speaking to Suzuki who I have to say were about as useful as a chocolate fire guard we were no closer to solving the problem.
In the end after putting nearly £15k in Suzuki’s pocket we took the problem on our selves to sort out.
We ended up going from a Suzuki 23’’ stainless steel prop that cost an arm and a leg, to a Turning Point 23’’ (aluminium) that cost les than £65. We took 1’’ of the pitch and its perfect, no slip, better pick up and a far better top speed.

Lasermatrix · 23 August 2006, 08:29

I also have a DF140 and have a S/S 21" prop, WOT gives me about 5500rpm and a speed of around 43knts.

I was actually wanting to try a 19" prop to see if I could get a little more top end out of it.

Sorry guys, I'm not a ribnobber, but a hard boater, but I do like ribs, honest

The engine is rigged to a Shakesphere 610/Ring 20 hull.

jwalker · 23 August 2006, 09:27

Quote:

Originally Posted by Lasermatrix

I also have a DF140 and have a S/S 21" prop, WOT gives me about 5500rpm and a speed of around 43knts.

That's a slip of -7.66.......

Quote:

I was actually wanting to try a 19" prop to see if I could get a little more top end out of it.

You wont but you might get a better lower end.

Lasermatrix · 23 August 2006, 10:13

Quote:

Originally Posted by jwalker

That's a slip of -7.66.......

*wanders off grumbling about inaccurate readings*

Hmmm, methinks I had better check my RPM guage out

Negative slip....that's not supposed to happen

toby4594 · 23 August 2006, 18:44

Called steel devs today, was hoping that they would have been a bit more helpful the best they can do is a 1" repitch at half price so down to a 22". Original cost with postage and the dreaded £304-00, repitch plus postage both ways approx £48-00 Costly prop this. Theres a lesson here, beg ,borrow or steal prop to try before you buy.

Hightower · 23 August 2006, 19:03

Sorry to hear of your problems, it's always is better to borrow or even buy second hand. If you want to try a different prop then a Thread here asking if anyone is local and can help is always worth a try first.

I was lucky and bought a couple of differently pitched brand new alloy props back from a trip to the States and after a very kind Gent from Port Solent let me brorrow a couple of SS ones I had made my choice. After I selected the ones I wanted I sold off the props I didn't want and acually made some money.

Toby I have a 90 on a 5.3m RIB and can't run anything over a 17" alloy prop. Would a 19" SS prop be better for you?

jwalker · 23 August 2006, 21:11

Quote:

Originally Posted by toby4594

Theres a lesson here, beg ,borrow or steal prop to try before you buy.

And don't trust what someone who is about to make money out of you, tells you.

jwalker · 23 August 2006, 21:50

If I may make an observation here; I'm not familiar with the Suzi 140 but I feel you guys are maybe thinking in the wrong direction. The motor is about 2lt, normally aspirated and 140hp. That's a good power from a smallish engine and I'd bet the low end torque is not particularly high so the power delivery is going to be a bit peaky. Since most of the time you're not likely to be driving flat out, why not prop the motor for good low to midrange performance, ie. good holding, good acceleration, good grip while climbing the back of a wave etc., all the things ribs should excel at? If it were me, I'd be aiming to choose a prop which runs close to maximum revs when flat out, which I believe is 6200rpm.

Cruising revs will be a bit higher but the throttle will likely be less open because the engine will be lighter loaded and I'd bet you'll see very little difference in fuel consumption. It could even be better. Over pitching for relaxing cruise is a bit like leaving your car in too high a gear for most of your driving and when you come to the hills, you're fekked. It's also not best for the engine.

I used to have the Suzi 200 which was 2.7lt and a long stroke hence high low/mid torque and it's outstanding, and very satisfying, characteristic was mid range grunt. It gave me far more driving pleasure than an extra knot flat out.

It was the same motor that Codprawn has and although I've never spoken to him I'll bet he will confirm my experience.

So, forget the top end, get the midrange right it's just better boating.

Now, the new 150hp Suzi looks interesting cos it's 3ltr. Just 10hp more but I bet it pulls like a train.

Just my thoughts.

Alex Brown · 23 August 2006, 22:26

Apart from the Suzuki Ali Prop not biting quite so nicely, I have found it to be pretty much the same as the equiv 21" stainless prop I have on there now, in terms of both speed and engine revs. As it stands, on a good day, with 2 people, the thing will reach 6000revs at 43knots, a bad day with 9 people on, it'll do maybe 5500revs at 34knots, both figures at WOT. I am certainly not going to be trying a 23" prop, but it's fair to say that a 19" would get the revs easily upto the 6200 mark.... but this is quite high for a 4-stroke marinised car engine though isn't it? Even 6000revs is high.... the boat cruises nicely around 22-26knots at 4200revs.

I wouldn't mind the 150 suzuki now though - that thing I'm sure would get at least a few extra knots out of the destroyer hull.

Many years ago, I did my L1 and 2 on a Destroyer 7m with Johnson 200hp Venom on the back - talk about fast, soft and dry.... it was then that it was Destoyer that was chosen

-Alex