A stupid question about planing?

[wahnamch]

My apologies in advance if this post is/seems stupid .... I just don't know where to start.

Setup:
1984 Cranchi Hobby 190 (19 feet)
Volvo Penta AQ175A (should be 170 HP?)
Volvo Penta outdrive (I think 280 -- how can I identify that?)
If the outdrive is indeed a 280, it should have a ratio of 1.61:1 from what I have found through searching

Boat is about 1250 kg with engine
Usually carry 3 to 4 adults with half a tank (120 litre tank)
Sometimes use it for water-skiing (2-3 adults in boat, 1 on the rope )
Prop -- no idea except that it has 3 blades and is painted the same colour as the outdrive (probably steel?)
Prop condition -- ok - a couple of minor nicks as far as I have seen

If needed, I can get WOT rpm and speed this weekend. How should I load the boat to get these numbers? (must remember to take my GPS with me as the speedo doesn't work at the moment)

Boat is (and in its life as far as we know) only run in fresh water (lakes in the Swiss alpine region.

Problem:
If I get the terminology right: hole shot and speed to plane

With 4 adults in the boat it seems to take "ages" to get on plane
With a heavier adult (say 80kg) on the ski-rope, 2 adults sitting up front of the cockpit (not a bow-rider, engine is aft), we can JUST about pull the skier out of the water (mono-ski). Once up, there is no problem as long as we plane out quick enough.
Top speed is not an issue for us as long as it's enough for the skier

So, if I could ask for some help on:
- Finding out what the boat SHOULD be able to achieve
and
- How I can best achieve it
that would be much appreciated.

Sorry again if any of this comes across as stupid in any way. And thanks again in advance for any help anyone can offer.​

 

[hwsiii]

Re: A stupid question about planing?

Wahnamch, none of the questions you are asking are stupid, you just don't have knowledge in this area. Nobody can help much without knowing what prop pitch and gear ratio you have. We also need to have some wide open throttle numbers with the accompanying RPM and GPS speed data.
I can tell you right now that you have a prop with too much pitch or blade geometry for what you are using it for. What are the recommended WOT RPM for your motor and what are the maximum RPM you are attaining with it now with 4 people in the boat. If you don't know this right now get it for us this weekend and come back and post it.
I just wrote a little article on how to measure prop pitch if you don't know it, if you will go here you can see how it is done and then tell us what you have.

http://forums.iboats.com/showthread.php?t=332091


H

 

[wahnamch]

Re: A stupid question about planing?

hwsiii,​

Thanks so much for the quick and encouraging reply. By the way, my name's Andrew ​

I have done another search and found http://forums.iboats.com/showthread.php?p=475364 which says max. rpm is 4800 and volvo (http://www.volvo.com/volvopenta/uk/...duction_engines/out_of_production_engines.htm) confirms that. So that's at least one piece of information found:redface:. And according to that site, it must be a 280B outdrive with 1.61:1 Ratio.​

Thanks also for pointing me to your informative article. Sadly, I don't have the possibility to take the boat out to measure the propeller. Is there another way to find out what I have? Could there be markings on it somewhere (visible when mounted)? Or do I have to remove the propeller (in the water --- can that even be done?)?​

 

[hwsiii]

Re: A stupid question about planing?

Some of the time it is on the side of the prop and some of the time it is under the nut holding the prop on or it can be at the rear inside of the prop. It is hard to say. You might find it without having to take it off. And yes the propeller can be removed while it is in the water, just trim the drive up so you can see everything.

H

 

[wahnamch]

Re: A stupid question about planing?

Thanks again ... and wish me luck!​

 

[hwsiii]

Re: A stupid question about planing?

I will Andrew, hopefully it will be on the side of the prop where you an just read it.

H

 

[wahnamch]

Re: A stupid question about planing?

Some good news and some less good news:

Can't get the propeller off and ther are no visible markings . The locking Allen key is REALLY blocked. I can't budge it.

The diameter is 15" (as far as I can measure). I tried to measure depth (front to back) but that is not so easy in (under) the water. It looks like about 3 1/2 inches (but I can't guarantee that number). It is impossible to measure the angle, though.

We took her out for a spin and got:
3800 rpm WOT resulting in 30 mph (50 km/h) on GPS

I found a different prop lying around with the markings:
VP837
15x17R
393FA
854148 the 48 is a guess as the marking is not perfectly legible.

Is that enough to get started with?

If we need more, I'll need to find a way to get the prop off. And that will mean take it out I guess (and our mechanic is away for the next couple of weeks).​

 

[hwsiii]

Re: A stupid question about planing?

Andrew, it appears to me that is a Michigan Wheel prop and that is very close to the one you need for your boat,with all the information you have given me so far. Here are my numbers for your boat.

Boat and Motor

Prop Picker

I am trying to send you some pictures but photobucket is not working right now.


H

 

[wahnamch]

Re: A stupid question about planing?

Thanks for all your trouble on this. It is much appreciated.

Assuming the prop is right (or near enough), is there anything else I can do to improve on hole shot and speed to plane?​

 

[hwsiii]

Re: A stupid question about planing?

Yes you can, if you will look back at my earlier posting you will find that I was able to finally post my numbers for you. Take the boat out and run it with the prop that is on it now and give me speed and RPM numbers from 3,000 RPM up to wide open throttle, in increments of 500 RPM. Then I will take those numbers and try to figure out which prop you have on it now, so we can see what we need to do for better holeshot and acceleration.


H

 

[wahnamch]

Re: A stupid question about planing?

Thanks again for all your trouble. As the weekend is over, it'll be next weekend until I can get the new numbers up. I will come back as soon as I have more input.

By the way, the other prop that was lying around didn't come with the boat (as far as I know). The hub length is shorter than the prop which is on the boat now.​

 

[hwsiii]

Re: A stupid question about planing?

I understand, I will be ready when you have the new numbers.


H

 

[wahnamch]

Re: A stupid question about planing?

Thanks again. By the way, I have found out the boat is 1150 kg (not 1250). I also found a German forum where they were talking about this same engine and a similar boat size and weight delivering 65km/h at 4400 rpm.

Engine weighs in at approx. 350 kg (included in the weight above).

Just in case this is of any help.​

 

[QC]

Re: A stupid question about planing?

lakes in the Swiss alpine region.

I saw a comparison to a German boat of similar power. Just a mini-warning. Altitude differences can make this comparison completely invalid. You need to get the prop right no matter what, but I would hate to see you chase any engine performance concerns if it is altitude that is making the WOT numbers low . . . just didn't see that addressed here.

 

[wahnamch]

Re: A stupid question about planing?

Thanks for your input and concern. The lake in question is only about 300m above sea level, though.​

 

[hwsiii]

Re: A stupid question about planing?

QC, you are 100% right it can make for major differences in performance .



H

 

[wahnamch]

Re: A stupid question about planing?

I finally got out again. Now I have a strange phenomenon --- the rev counter is inconsistent and not stable.

I had 4200 rpm for a while (NOT WOT) and then it dropped to 3500. When running slower, I was at 3300 for a while and then it "skipped and jumped" and went down to 2200! By the way, the speed didn't change with the jumping around of the rev counter.

I'm afraid I don't think I can provide any reliable information apart from what my GPS tells me. But that, if I understand rightly, is useless without the relevant rpm data to accompany it.

Oh well -- I guess I'll try and get the rev counter fixed first before "worrying" about the prop.​

 

[hwsiii]

Re: A stupid question about planing?

Wahn, take the switch on the back of the tach and turn it back and forth a few times, some of the time this will cure the problem, as corrosion will mess up the electrical contacts on the back of the tach. Just make sure it goes back in the same position it was.


H

 

[oshkoshboating]

Re: A stupid question about planing?

hwsiii, where did you get that spreadsheet? did you make that? (I am drooling over it!)

 

[hwsiii]

Re: A stupid question about planing?

Yes I did, spent a long time doing it to. Just trying to get it perfect now.


H