Yamaha 225

Hi guys,

after speaking with quite a lot of boat people, it seems like propellers can change their pitch angle... Is this true? One said that the Bravo 4 blades tend to lean foreward after about 100 houres from new giving less pitch. It seems strange to me but.... what is the real fact here?

For example, my own boat, a 29 Fountain with twin Scorpion 377s ran 83 mph at 5400 rpms at the Fountain factory when new. I bought it when it was 3 years old an it had 60 houres on it. The boat never ran more than 78 even if I had 5500 rpms (it has 1,65:1 gears). That is a difference of 5 miles per houre! 5 miles, and 100 rpm more... I thought I might be running in the rev limiter even if the red indicator lights did not come on because the bow seemed to drop just a little bit after 10-15 seconds at full throttle (when I reached 5500 rpm) leading me to believe the power decreased a bit if it had a gradual rev limiter reducing the pre-timing in the ignnition or something like that.

So I put on 32" instead. It still ran in the 5400-5500 range but now the speed was up to 82 mph at its best run.

SO HOW IS IT POSSIBLE that the boat ran 83 mph when new with the 30" props????? I spoke to the guy who owned it before me, and he also said the boat ran 83 back then. It never came above 78-79 no matter what I tried when it came to my ownership here in Norway.

HAS THE BLADES GOT A DIFFERENT SHAPE?

Also Nor-Tech has said that the blades have been "bent back" in big diesel powered boats.

One other experience that makes me believe they change is this: In the autumn we drove a 35 Executioner with twin 496 HOs at 78 mph (clean boat, no barnacles). Then, we put the boat in winter storage. The spring after, we put her out again. Now the boat ran 78 mph again, but thre red lights were on constantly as we were running 5250 rpms which is in the rec limiter on 496 HOs. How is that possible? No one has ever touched the boat in its storage as I had it in my workshop under full control.

I WANT TO KNOW THIS!!

Perlmudder

hmm interesting! im curious to see what people say.

spazboz

iTrader: (2)

To be honest, thats someting I've never thought of before... Good Question!

CB-BLR

I believe that as props are used, that the metal fatigues, and that they do indeed change pitch over a period of time. Some props even get weak enough that the metal fatigue causes them to break or throw a blade. The better the metal and manufacturing, the longer this seems to take.

Chris

tomas_wallin

In the fall the boat weighed alot more than when you put her in in the spring. The gelcoat and polyester attracts water so that boat could have gained a few hundred punds after sitting in the water for one season. When you put her in in the spring the polyester has dried and the boat weighed alot less.

The extra weight changes the CG and how the boat rides in the water.

Yamaha 225

YES Thomas, that is a possible reason, but I don't think it will have THAT much to say for the top speed... Have you experienced this? The speed in autumn was exactly the same as on the factory even if the boat had been out a good summer. One possible reason could be that the boat was dialed in at the factory, but as these engine had approx 70-80 houres after that first season, they became fully broken in, but why is that happening right at that time.. My own boat goes just as fast even after being in the water a full summer! This is the boat that I sold to one guy in Saltsjöbaden in Stockholm. You might have seen it!! Was at the Cape North race. :-)

There is just no real answer to this a elieve, but something must have changed. The case for the rpma autumn and spring would make sense with water being sucked up in the gel coat. But the case for my 29 Fever and the speed/rpms new and afer 60 houres with the same props still don't make sense unless the props have changed the pitch angle. No one have touched the oat excpet myself!


Going out for a last run with it today right now!!

Velocity Vector

iTrader: (4)

Are those real numbers from the factory or advertised numbers? My advertised numbers on my 320 Velocity was 85 but never saw over 80.

Yamaha 225

These are actual number for this spcific boat. t also showed 83 mph on the GPS tattle tale.

Griff

You said the boat was 3 years old when you got it. I would be willing to bet that the props are not the same ones that the boat was tested with.

Yes, props may flex a little over time, but I do not believe to the extent you are seeing. Labbed props are thinner and I have had freinds loose 1-2mph after a couple seasons, then send them back in to be brought back to specs.

If you're seeing 82 with the 32's then keep them.

bbladesprops

Surprised this never came up over the years. I believe it may have in other semi related threads.

Yes, blades do become "laid back". This does two things. Decreases pitch progression slightly at the larger radius's and allows the water to fall off the blades easier. Problem #2, cups can get washed out. The cups can control the waters release. As the cups wash out, the water can release quicker and the rpms go up and speed can fall. Sand and muck are tough on cups (trailing edges).

Having props tuned at regular intervals is important if you notice performance losses. Especially with Labbed props. However, it isn't always the propellers fault......I live with that issue every day HAHA.

Brett

Brett