getting onto the plane

[Spi D]

Not good. Depending on the fault code shown it regards something in the engine electrical system.

You mentioned your engine, so we now know that you are running a single Volvo D3-190. This 5-cyl 2.4 litre engine develops 180 hp @ 4000 rpm on the propshaft and the recommended rpm range at WOT is 3800-4100, so your aim with normal load is the 4100.

The engine was delivered with either single prop SX-M1, Duo-prop DP-S or XDP-B sterndrive and gear ratio inside is 1.51, 1.66, 1.95 or 2.11 so you will have one of these.

 

[MapisM]

One thing to look for is the props 'grip'.

Never heard of such concept. How do you measure it, as the complementary percentage of the slip?
I mean, if you have a setup (hull/transmission/prop) whose slip is 10%, would you call that a 90% 'grip'?
Just curious.

 

[Greg2]

FWIW I always have the legs on my boat all the way in as no matter what speed I am cruising at, the speed drops as soon as I trim them out...

Is that wrong?

On our Targa 35 I hardly ever altered the leg trim. Kept them tucked right in because trimming them out made little/no difference. Previous owner found the same.

 

[MapisM]

Well, if the hull kept the same attitude with a "wrong" thrust direction, it means that it was well designed, and not much sensible to trim.
It doesn't mean that keeping the drive always lowered was the right thing to do, though. If nothing else, at cruising speed, for any given RPM/speed, you will have run the engines at a slightly higher load - hence with higher consumption.
An horizontal thrust is always bound to be more efficient, that's simple physics.

 

[Spi D]

Different propeller designs provide different properties.
Rake, blade area, blade shape, number of blades combined with cupping and shape of leading and trailing edge, plus various amounts of controlled ventilation over the blades, are some of the parameters in play when designers aim for a propeller's use.

Examples:
Some props are designed to run in an air/water blend and accepts surface breaking, some provide lift to the stern and others to the bow. Large area props for heavy loads, small area props for extreme speeds.

If a boat and engine setup tends to ventilate a prop design that either accepts this or eliminate the problem can be chosen.



Grip is not the same as slip or defined by a measure, but describes the props ability keep producing high thrust even under the most demanding conditions. Pretty much like different car tyres providing different friction under different conditions - and not only due to different thread layouts.

Ofcourse the propeller's ability to influence the boats behaviour depends on the boat size in relation the propeller(s), power available and possible trim adjustments (therefore irrelevant to shaft driven boats).

For detailed information, this free book by Quicksilver is recommended:

http://spidybot.com/prop_/Quicksilver_Propellers.pdf

 

[El Bee]

Different propeller designs provide different properties.

<snip>

For detailed information, this free book by Quicksilver is recommended:

http://spidybot.com/prop_/Quicksilver_Propellers.pdf

Brilliant, I've never seen so much info on props in one place!

Many thanks

Lee B

 

[MapisM]

Grip is not the same as slip or defined by a measure, but describes the props ability keep producing high thrust even under the most demanding conditions. Pretty much like different car tyres providing different friction under different conditions - and not only due to different thread layouts.

Huh?
With my previous question, I thought it was just a matter of semantic, but now I'm wondering if I'm discovering something which I've never heard of in decades of boating, or you're just using colloquial concepts which have nothing to see with engineering.
I suspect that the latter is true though, considering that as you say this 'grip' is unmeasurable...

Anyway, fwiw, the booklet you linked doesn't even mention the prop 'grip', whilst there's an entire chapter dedicated to slip.
That aside, I'm afraid it's a bit outdated, after 20 years from its publication.
Just as an example, it states that ...Referring to the use of non-racing stern drives, the "X" dimension is raised on fast, conventional single-drive boats by 1" to 2".
And it follows explaining that with higher X-dim, insufficient cooling water is a major concern.
Now, my non-racing stern drive, factory installed on a fast, conventional single drive boat, has an X-dim which is raised by almost 5".
And re. cooling water, I guess that they wrote that booklet before Mercury itself invented the low water pickup...

All that said, if at the end of the day what you actually mean is that all of the prop characteristics (on top of the usual pitch and dia) should suit the hull need, then I fully agree, of course.

 

[Spi D]

Unfortunately propeller physics have not changed since invented. Funny enough, the prop design available for my first boat in 1968 is still around - now with the addition of plenty new.

What do you call it, when a prop is spinning fast in water but the boat does not move? Producing a lot of foam, but no real thrust?

The opposite is grip.

I suppose you noticed the duo-prop 'invention'? One of the main goals was to improve grip and it certainly did.

Low water pickup isn't new. As it isn't a standard equipment is does make sense to warn when discussing raised engines - not least when at a lift to adjust the X-dim while running.

For the sake of this thread's initial problem, I'll leave it at that.

 

[Searush]

I don't know how you can get a boat on the plane. I can't even get a bottle of pop or a second bag on one. AND I hate the two hour wait in the airport before I can get on it.

 

[MapisM]

What do you call it, when a prop is spinning fast in water but the boat does not move? Producing a lot of foam, but no real thrust?

Ermm... slip, of course - whatever the reason behind it, cavitation, ventilation, or whatever.
Anyway, in your example what we have is a 100% slip, period.
Since you now say that grip is the opposite, I suppose it's correct to say that grip is zero, which brings us back to my initial understanding.
Anyway, I agree that for the sake of this thread, neither slip nor grip are going to be of any use to the OP, unless you're aware of any props for VP outdrives with a better 'grip' than the OEM ones...