Changed Drive Shaft ????????

[Peterjfinch]

Hi Burty,

There's a video of the engine possition here.

http://www.youtube.com/watch?v=WdYlWXw8Sv4

It shows the engine level, with depth of bullet compared to bottom of hull.

Peter

[Peterjfinch]

Johnny, where do you think the speed has gone?

[JamesM]

Up in the air with all that water?

What prop have you got?

What RPM at what speed?

[Peterjfinch]

Johnny, It's a Laser II, 21, 52MPH 5600 RPM. Was getting 57.3MPH with the 25" leg but had too much chine walk. Now she runs level but slower

[roofer]

I'd try a 22 chopper, looks like you've got to much hull in the water, you need a bow lifting prop to get some air under boat.

[the bandit]

So it only does 53, look on the bright side its got a pretty good rooster tail for a laser prop.

[marshan162]

Hi peter

Does it feel slower? How are you measuring the speed GPS or water pickup on the lower unit, if the later, is that now not in good clean water possibly

What revs were you getting before at 59 MPH, becauase at present assuming a 1.87 ratio gearbox your prop slip is coming out at 12.5%, which is not really bad.
If you were doing 59 MPH before with the same revs, your slip works out at less than 1%(impossible). So i would guess either a speedo reading discrepency or the motor is not pulling its weight anymore. Now the motor should be revving higher with the prop up higher. Can you remember the revs when the motor was low? Also can you confirm your gear ratio of 1.87

Karl

[marshan162]

As for the water pressure, temporarilly block off the two uppermost pickup holes , a bit of waterproof gaffer tape may do the job as a test

[Peterjfinch]

Hi Karl, Yes it does feel slower. Both speed records have been from the same (fitted) GPS. Not sure what the RPM was, I was too busy worrying that the boat was going onto it's side. The earlier speed was 57.3. The gear ratio is whatever is standard, I beleive it's 1.87. I just can't work out where the speed has gone. If I leave it trimmed about level, it bounces up and down like a nutter. As you can see from the video, it still does slightly and I was under the impression that trimmimg out / up, should get rid of that and get her running right.

Peter

[marshan162]

Peter I just had a look at your pictures of your rebuild, is your fuel tank upfront? You may be better off with it in the rear.

[Peterjfinch]

Karl, did you look at

http://www.youtube.com/watch?v=WdYlWXw8Sv4

it shows that the bottom holes are above the bottom of the hull. I have been quoted around 70 - 75 MPH from this setup, why such a shortfall? engine, weight, prop??????

[Peterjfinch]

Karl, Fuel tank runs from front (under dash) back to about 6" short of transom. I only had about 70ltrs in her yesterday.

[marshan162]

The puzzle is, your revs before with the prop burried must have been higher, otherwise you would have had close to zero slip. It doesn't sound right that now with the engine higher, the revs have dropped. I'm wondering if she was getting a bit too hot and was down on power. The theory about blocking off the highest two holes is to stop it sucking air.

As its positioned your probably running a bit of a riskof cooking the motor. Is the motor as low as it can possibly go

[Peterjfinch]

Hi Karl,

Yes, the engine is at it's lowest. Could I adapt something to deflect water up to the intake, as a trial. I think I have to order the nose cone. There has been a suggestion, that it could be a hub problem, a spun hub. What do you think and how can I check it?

Peter

[Peterjfinch]

Hi All,

Could the problem be, that the Laser II does not perform as well on the surface, as it does below (with the 25" mid). Just a thought. Problem is, unless I buy another prop, I wont know, would anyone on here know. Wish I were in the UK for a month, with boat.

Peter

[marshan162]

With a 21p prop half out the water I think the revs would be a lot higher than 5600 if the hub was slipping. All assuming the tacho is accurate of course.
Does the engine note sound similar or faster than before, I know it's probably difficult to remember.

Anyone got a P21 with a 200 and a 21p prop to compare speed/revs

Just wondering if you could perhaps fix something on the intake and feed it with your bilge pump from a hose in the water. Perhaps glue some muff cups on. Just for testing of course

Have you measured your transom hight, it looks very high

[Peterjfinch]

Karl,

Transom is exactly 25", 90 degrees to hull bottom. If I fitted something like a pair of muffs, with the pipe facing forwards, with a funnel in it, that sort of setup??????

I would have thought there were many people on here, with P21's, that know. Maybe they've not seen the thread.

Couldn't be sure about the sound of the engine, sorry.

Peter

[Burty]

dude, i think that its a setup problem, more to do with fuel tank being up front, when the prop was low in the water bow lift wasnt a problem but now its almost surface piercing it can not create enough lift to get the nose out of the water hence the more you trim out the bigger rooster you get. i suggest you move the fuel tank to the back and try again. maybe get a temperary 20ltr tank and stick it behind the back seats, empty the front tank and see what happens. I'm over in your area at end of may so if still having problems maybe i could bring a different prop for you to try of just have a look at your setup.

Rob

[marshan162]

You could fabricate a transom pickup until your nosecone arrives, all you need is a fitting to go into the pump. If you go to Bobs machine shop site they sell kits. All they consist of is a piece of pipe fixed to the transom with a forward facing aperture Go here http://www.bobsmachine.com/

[marshan162]

Just measured the transom on my Marshan and it's about 21", 25" seems high. Does it look like there has been an addition to it., especially considering that originally your boat yard told you to buy a 25" motor

Have you got a fat mate who can sit in the back?