Proper prop selection for 466 MY in Fresh water?

[carvergofast]

Looking for some experience on prop selection for my 466 in fresh water. I previously ran the boat in saltwater where WOT was about 2655 rpm @ 26 mph. The props have recently been reworked (28 x 28) and are very smooth running, however I am not seeing the speed that I have seen on the specs for he 466 of 32 mph with 1-2 foot seas. Since we hve moved the boat to fresh water my WOT is around 2450 rpm and my speed is only around 23 mph. Now I understand this isn't a speed boat, but I am looking for optimal fuel efficiency and performance.
I have heard that you may have to drop two pitch sizes to achieve the proper WOT. If anyone has input on this I would sure appreciate it. Also FYI, I am running the Volvo 74 TAMD's
480 HP, and they appear to be running well. Thanks

[waybomb]

How about elevation? Less dense air makes less horsepower, but I think you can tune the controls for the altitude.
And what about the fuel you are now using - is it the same as what you used to use, or does it have a different emissions package?

After that gets all sorted out, call a prop shop. They'll give you a form for recording a bunch of data - rpms, speed, etc. From that, they can suggest a repitch of the prop, if needed.

Make sure your bottom is clean too. Your boat bottom.

[carvergofast]

Hey waybomb, thanks for the reply. All the things you speak of have been addressed pretty much, went from sealevel to 680', bottom just done, engines all scanned, filters changed, etc.
Have driven the boat 4 more times since the post and no matter how I slice it, I get 23.4 GPS. engines are running great with no smoke, but lost 250 rpm from saltwater to fresh. It is right at the critical speed of planning out. I will get with some prop shops and see what they can come up with, maybe Carver can assist as well. Thanks again

[uaesi]

Hi, I am new to this forum and last year purchased a 466. We have only put 40 hours on the boat... but it is in fresh water so I hope i can help out. Our 466 is a 2004 model with same HP Volvo engines. Our typical WOT is 2650 (Never really tracked GPS speed but I think it was 24-25 GPS)...so that puts a flaw in your low RPM theory? I did ding 1 prop late in the year and have them in for repair and rebalancing while the boat is layed up for winter.The Props pulled were imprinted as 28 X 29.5. I did find out the props are a "progressive pitch" with a "mean pitch" of 30.5. From the factory my props were 28 X 30.9. The repair shop for my props coordinated there questions thru Carver which sent them to ZF Marine. In the spring I can update performance but for now we're frozen in!

[carvergofast]

uaesi, thanks for the feedback on your Carver. How did your boat perform after having the props repaired? Thanks

[uaesi]

Sorry for the slow reply! My current props get 2650 RPM's and are the 28 X 29.5's GPS speed varies with load, current on river, etc. but is about 22-24 mph on a GPS. I have been noticing these boats (quite common) having the same power with 28x32 Teignbridge 4-blade Aquaskew props? I would think the higher pitch will get you more speed but lower the RPM's? Do we dare re pitch to 32's? Anyone out there with ideas? I agree it would be nice to know the optimum prop for the 480 Volvos in this boat!

[Lyndon670]

You might want to read the blog called "report from the bilge" - Google it, interesting read. Now, it is on a 506 but - the specs aren't going to be much different. My WOT on my 2001 506 with the TAMD Volvos gets me 2600rpm reaching 22mph on the GPS with a 2300 cruise at 18mph. You will find that the fuel curve on the 480s won't change much the faster you go - each 50rpm works out to be 1 additional knot past cruise. I find for me, 2200 RPM at 16mph is a comfortable speed....

[uaesi]

Thank you Lyndon! Excellent article and I will save it for the archives!! It does tell me I "maybe" should try the 28X32's as factory tested. My boat gets plenty of power but I feel it is underpitched with 28X29.5's and, as they are not the originals, it makes me wonder?
I will definately check that sensor for the drain hole!
The article should help Carvergofast evaluate his condition as he may have something else going on.

[Lyndon670]

That sensor you are speaking about - I have part numbers if you need them. I had both replaced on mine as per the Volvo service bulletin. It's a simple job and inexpensive. Also check your swim platform - the seal goes (underneath) and it fills with water (can't remember if that was in the article), I had probably 60 gallons in mine just from the trip from Toronto to Lake Simcoe (280 miles). At 10lbs per gallon, that's 600lbs hanging over the swim platform.