Proper cruising RPM's

[WTR4FUN]

I have a 2001 Monterey 180 Edge, equipped with a 4.3 vp rated at 190 hp. The owners manual says that WOT max rpm's are 4200-4600. Can anyone tell me what an average cruising rpm would be? Is there a formula typically used to determine this? I do know that rpm's can be affected by pitch of the prop, trim position and load on the boat, im just looking for an average as a starting point. Any help would be appreciated.

Thanks

 

[QC]

Re: Proper cruising RPM's

Hey WTRFUN, welcome aboard!!

I have moved this to the I/O section as it is really not a prop question. Personally I think "Cruise RPM" is somewhat arbitrary. I like 80% of Wide open throttle RPM. Some guys say 75% of throttle, but what the flip is that? You going to measure the throttle plate travel inside the carb? I don't think so . . . I believe both Volvo, and I know Merc, say you can run them at WOT forever, but they suggest that ultimately life will be shortened. If it is fuel economy you are after, that is yet another answer, and with your boat I am guessing 3500 RPM . . . So there you go, opinions are like azz . . .

 

[tombstone]

Re: Proper cruising RPM's

Many yrs. ago had the same question which was asked of an experience marine mechanic. His answer was 3200 rpm. I use 3000-3200 for best mpg and eng. is barely breaking a sweat.

 

[WTR4FUN]

Re: Proper cruising RPM's

Hey no problem moving the thread, I was a little unsure where to post because I am still getting used to this forum. Right now it seems like I have to keep the boat around 4000-4200 just to stay between 25 and 30 mph. AT 3200- 3500 im barely on plane and probably going around 15-20 mph. That does not seem right to me. The boat has a "dry" weight of 2000lbs, I typically have 2 adults and 4 small kids so I dont think im overloading the boat. The p.o. installed a stingray on the outdrive, will this affect cruising or top speed? Also the boat seems to just chug gas. I would like to see 30 at around 3500 rpm, does anyone think that is reasonable without making the boat to sluggish? I appreciate any advise or opinions.

thanks

 

[IVAZ]

Re: Proper cruising RPM's

You need to verify that your tach and speedo are working correctly. I think it should be faster than 25 at that RPM.
The foil will get you on a plane a little faster but, it has many other issues with it. When I took the foil out of another boat I had it picked up 4mph at wot. Getting on plane was marginally worse. I would say you have more issues than just the foil though.

 

[steelespike]

Re: Proper cruising RPM's

Heres the deal from what I've seen and read here.
imo,the best cruising speed, best practical speed and economy,
can be at just on plane or signifigantly higher.Vague; yes. Best way to determine most efficient is to keep a carefull record of your time at a given rpm or to a favorite destination.Distance isn't figured like a car you want the lowests fuel consumption. Top up the tank to figure the number of gallons.Your looking for the lowest GPH(gallons per hour)A pain to say the least.Most pick a speed they like and go with it.Of course a flow meter can really simplify the process.

 

[wired1236]

Re: Proper cruising RPM's

To help with a comparison, I have a '07 Reinell 185 (18.5') with the same engine, a 4 blade 19" SS prop, weigh the same as you, and have the same family load. Before I put on smart tabs, I could get 25mph at 3000rpm and stay on plane in the high teens going around 2500rpm. Now with the smart tabs, I can get on plane right away at 2000rpm and stay there around 12mph! These are approximate numbers but they should give you the idea that you can do better.

I would look into smart tabs, check your tach, and look into prop changes, (not sure what prop you have).

Hope the comparison helps.

 

[WTR4FUN]

Re: Proper cruising RPM's

I have heard nothing but good things about the smart tabs and definately think I will purchase a pair down the road.(if my transom will accept them)Right now im thinking I need to change my prop. I have never seen 40 mph with this boat and have had it on the top side of the safe WOT rpm's. It did not have any trouble getting there either and seemed to have more to give.

 

[180shabah]

Re: Proper cruising RPM's

We need to know what you have to start with.

What prop are you running? What are your WOT numbers? Speed and RPM.

If the number you gave above are accurate you are probably underpropped - previous owner may have been into wakeboarding and such.

If geared and propped correctly, small boats with 4.3's usually fall pretty close to 3500RPM for best cruise economy. Of course this is just a starting point, you will have to experiment to find the best cruise for your particular boat.

 

[WTR4FUN]

Re: Proper cruising RPM's

The boat currently has an aluminum 14.5x19 prop. The out drive is a vp sx-m with a 1.79 ratio. The boat came with a spare prop wich is a 14.25x23. I think I will swap them out and remove the stingray and see what happens. Thanks for the feed back.