Question for CD 25 owners with a 150 Yamaha

alainP

What prop size and pitch are you using when in full cruising mode (heavily loaded that is) and at sea level? What max rpm do you achieve with that prop? my 15 1/4 x 15 is not to snuff I am thinking of trying a 15.5 x 13.

thataway · Posted: Sun Jun 23, 2019 6:29 pm Post subject:

What RPM at WOT and what is the WOT speed in statute or nautical MPH? Is the boat heavy or light loaded? Is your prop aluminum or SS, much cup, or none?

If you ever run your boat at higher altitude you will want the lower pitch--or even lower. than 13".

alainP · Posted: Sun Jun 23, 2019 9:33 pm Post subject:

The boat is mostly heavily loaded, aluminum prop, 0n a good day I'll get to 5k @ WOT playing around with tabs and motor trim. I usually reach high teens in knots then. This is all at sea level when sea conditions allow, hard to find a day with really flat water though, I am sure That makes a difference. As for the amount of cup, it looks like there might be some, I really don't know what constitute a lot or a little in that domain. I always seem to be stern heavy even with 150 fr of chain in the locker, I do have Permatrim on the Yamaha. How many rpm could I expect to gain going to a 13 inch pitch?

thataway · Posted: Mon Jun 24, 2019 11:20 pm Post subject:

The rule of thumb is that you get 200 to 300 RPM per 2" crop in pitch. But @ cup can make 100 RPM. SS will run better than Aluminums with less "flex".

You are at the low end of RPM for that motor. I would definitely drop to a 13". Is the Permatrim right on the surface of the water? That is where it belongs. If it is buried, then the engine may need to come up a hole or two....Too deep, will slow down.

For example, with a Honda 150, and 15" prop pitch, I get about 5000 and in the 20 mph range when fully loaded for a long cruise. As I use water, fuel, etc, even with the same gear, I can get up to 5500 and 25 mph. When the boat is light, I get 6000 RPM, and 29.7 mph...depending.....So, do I prop for the heaviest load, or for the average. I choose the "middle".

alainP · Posted: Thu Jun 27, 2019 11:31 am Post subject:

I got the 13" yesterday, blades look a little flatter than the 15", we'll see what happens when back in the water. Thanks

colbysmith · Posted: Thu May 21, 2020 11:23 pm Post subject:

Alain, what did you find out going to the 13 pitch? I've got the Yamaha 150 on my new to me CD 25. Running it wide open today, I came up with about 32 mph, but at 5200 rpm. I'm probably going to order a new aluminum 15.25 x 13. Colby

alainP · Posted: Fri May 22, 2020 12:12 pm Post subject:

Colby, I found out two things, the gain in rpm at WOT seemed very modest but the noise it produced at low rpms was very annoying, The noise was like a rattling can full of gravel and would disappear at around 1900 rpm. i do too much displacement speed while cruising and fishing to put up with that, I went back to the 15 inch pitch and kept the 13 as spare. The prop was a basic Solas aluminum.
I always have a lot of weight up front, in the back and really everywhere. Finding a truly calm day in the Sea with flat waters, no wind or currents for testing props and rpms is rare, especially in the Winter or Spring. so..I gave up on further testing for now, too many other things to fuss with.
32 mph at 5200 rpm is pretty good, you must have been light?
Alain

colbysmith · Posted: Fri May 22, 2020 11:13 pm Post subject:

Had full tanks of fuel and water. But that was pretty much it. I'm still setting up the new boat to me. Colby

colbysmith · Posted: Tue Jun 02, 2020 12:03 am Post subject:

Before Alain had replied about his results with a new 13 pitch prop, I had already ordered one. For me, I was happy with the results. I ended up ordering a Solas 3 blade aluminum, 15 3/10 x 13. (The other one above was 3 blade aluminum as well.) Today, on a choppy lake, I was able to get a WOT of 5700 rpm (Yamaha specs recommend 5000-6000), and top out at about 30 mph. Again, it was choppy so on a calm lake I may have been able to trim up better and pick up a little more speed. However, I am happy with the 5700 RPM and 30 mph.

By the way Lew, (Cat's Claw), I cleared that bridge by 26"! lol. (I have a low bridge to go under on the way to the local lake state park ramp. Since it was relatively quiet on the park road, I took some measurements to learn C-Traveler's clearance on the trailer, mast light and antenna's down, but with a radar on the roof, was 9'-10".) Colby

thataway · Posted: Tue Jun 02, 2020 11:34 am Post subject:

Your RPM and speed sound right with 150 hp. As the boat gets heavier that will decrease.

Sometimes a very light chop will give even a faster speed.

alainP · Posted: Tue Jun 02, 2020 11:54 am Post subject:

Colby, are you getting that noise at low rpms with the 13?

colbysmith · Posted: Tue Jun 02, 2020 2:04 pm Post subject:

Hi Alain, nothing any different from the 15 as for any vibration or noise. I did get the solas rubber rubix hub as well, and that may help dampen any chatter. The prop I took off had the plastic hub. Colby

alainP · Posted: Tue Jun 02, 2020 2:43 pm Post subject:

I just looked Solas Rubex line of props, and..yes, that's what that insert is for, chatter and vibration!
Damn, i should have gone that way just didn't know.
Maybe we'll see you on lake powell?
Alain

colbysmith · Posted: Tue Jun 02, 2020 2:48 pm Post subject:

Possibly end of August first of September... Everything is up in the air now days. Colby