Large Wake

[smclear]

I just purchased a 1974 18' Century Resorter this summer. I absolutely love this boat. We had a 1970 16' Resorter when I was growing up. Anyway here is my problem. At idle speed the wake is much larger than I like. I would personally yell at anyone coming down our channel that was throwing up that kind of wake. Fortunately, every one on our channel has boat lifts but that's not the point. The boat currently turns about 4,400 RPM. This is exactly where it should be for a big block engine. Now, if I put a prop with less pitch on, it will go slower at idle. But, it will also allow the engine to achieve higher RPM's on the top end and that could potentially damage the engine. I know that larger (45+ feet) sometimes have trolling gears that slow the prop down allowing the boat to actually troll. My question is, has anyone heard of these things for small runabouts? The transmission is a velvet drive.

 

[tashasdaddy]

Re: Large Wake

what are your idle rpms? can you shift any weight to the bow? that boat should idle with almost no wake.

 

[smclear]

Re: Large Wake

It idles at 800 - 900 RPM, again, just right. The boat rides through the water perfectly. I do not want to put more weight forward. That could prove to be very detrimental at any other speed than idle. At any rate, I just found out that Velvet Drive makes a trolling transmission. I just don't know if they make one for my application. Their website suggests that they do, as they have pictures of similar size ski boats.

 

[jaxnjil]

Re: Large Wake

you stated you have a big block. mine is to and the idle speed on it is 650 to 700 as are most of the mercruiser of this age.
not knowing what you have for sure, this might not apply to you.
i'm surprised it shifts ok at that rpm. both this and my old boat shifted a lot better at the proper rpm.
not sure what you are calling a big wake but our boat will idle at 3mph,gps, and very little wake. the only trouble i have at that speed is steering. that is helped by running trim tabs all the way down.
i have found quite a difference in wake size in just going to 5 mph.

 

[smclear]

Re: Large Wake

you stated you have a big block. mine is to and the idle speed on it is 650 to 700 as are most of the mercruiser of this age.
not knowing what you have for sure, this might not apply to you.
i'm surprised it shifts ok at that rpm. both this and my old boat shifted a lot better at the proper rpm.
not sure what you are calling a big wake but our boat will idle at 3mph,gps, and very little wake. the only trouble i have at that speed is steering. that is helped by running trim tabs all the way down.
i have found quite a difference in wake size in just going to 5 mph.

Your boat has a Mercruiser I/O. Mine is a direct drive inboard. There is quite a difference. Mine also has a Velvet Drive transmission that shifts smoother than a babies bottom. I can absolutely guarantee it is running in tip top shape and idles at the proper RPM. It has been serviced by the same place since new. They have been in business since the early 1920's with a sterling reputation. He is also a neighbor who's word is like money in the bank.

If I were to take a guess, it puts out a wake approx. 8" tall!

All I/O's have steering issues at idle speed. I could put mine in gear point it straight and move to the back seat for the next hour or so and it will track straight as an arrow. Not that I would ever do that, but you can't do that in an I/O.

I could fix this easily by putting a prop on with less pitch. I am just worried that if I do that, the potential for higher RPM's at W.O.T. could damage the engine.

 

[abj87]

Re: Large Wake

I tend to notice that boats with shaft drives tend to have a higher headway speed than sterndrives. Thats due to them having (somtimes a lower reduction ratio), more stream lined drive, and not being stern heavy like I/0s hogging through the water at idle. Nothing you can really do other than lowering the idle a bit. That's a great setup you have, a LOT more desirable than an I/O!

 

[jaxnjil]

Re: Large Wake

sorry i missed the last sentence where you said velvet drive
i just looked in the mercuriser manual and under tune up. they show a 650 to 700 rpm in forward gear idle speed for a mie 340.
still not sure if thats close to what you have but your idle rpm still sound high to me
that said, i have checked my idle and set with a photo tack. i have found my boat tack to have 50 to 150 rpm swings at idle. sounds like your mechanic has you covered there any way.
now you have me on the 8" tall. to be honest i never looked at my wake with an eye to judge the hight in those terms. if i was to((( guess))) however i would say thats close to what we make. at a dead idle i'm sure its lower.
we run 4 to 5 mph in the no wake zones here and havent stood out any more than the other boats around us or had any complants.

 

[fixb52s]

Re: Large Wake

My little 178 with the 3.0 also throws a surprising wake at idle too. I would throw the kids in the bow while underway and it helps a little, but not much. My idle speed is around 7-750.​

I had a Supra Rider with the 454/velvet drive before, and at idle, it too would produce a little more wake than it should have. It would idle around 800 RPM. I never got around to playing with it too much thanks to the hurricane and tree a few years back. ​

There is really not much you can do with it other than say "sorry, but it IS at idle". If you can get the idle RPM down as stated before, that should help out a little.​

You can strap a mouse on a small wakeboard and throw it out on the rope when idling about. I would think that no one would say anything about your little wake with this setup.

BTW: here is a photo of my idle wake.

 

[salty87]

Re: Large Wake

that's a big powerplant for that boat. she must get up and go.

i've got a 454 (1987) in a 23' inboard...idle is 650-700.

sounds like you'll have to pop it in and out of gear if you can't get the rpm's down...trolling transmission sounds pricey

 

[Ned L]

Re: Large Wake

RPM was my first question too. 800 - 900 is pretty high, you should be able to get it quite a bit slower (& it will not affect the top end speed). If it were me I would try for between 500 & 600 RPM at idle.

edited to add --- Basically a big engine in a little boat isn't going to load the engine down when you drop it in gear, so it's not like it will stall at 500 - 600 RPM.
I have a 16' inboard with a Graymarine 109 (225 cid flat head six) and have it idle at 500 - 550 RPM.

 

[fixb52s]

Re: Large Wake

that's a big powerplant for that boat. she must get up and go.

i've got a 454 (1987) in a 23' inboard...idle is 650-700.

sounds like you'll have to pop it in and out of gear if you can't get the rpm's down...trolling transmission sounds pricey

Salty, you get your Supra back together yet?

 

[salty87]

Re: Large Wake

Salty, you get your Supra back together yet?

so close. kind of a bonehead move...my alignment had always been great. turns out that things had shifted over the years and my strut was mangled. had to hack thru the shaft to get things apart.

so, i had it on the water for about 3 mins, then straight back to the trailer. waiting for my new shaft and straightened-out strut.

this weekend should be it!...thanks for asking

 

[MikDee]

Re: Large Wake

My little 178 with the 3.0 also throws a surprising wake at idle too. I would throw the kids in the bow while underway and it helps a little, but not much. My idle speed is around 7-750.​

I had a Supra Rider with the 454/velvet drive before, and at idle, it too would produce a little more wake than it should have. It would idle around 800 RPM. I never got around to playing with it too much thanks to the hurricane and tree a few years back. ​

There is really not much you can do with it other than say "sorry, but it IS at idle". If you can get the idle RPM down as stated before, that should help out a little.​

You can strap a mouse on a small wakeboard and throw it out on the rope when idling about. I would think that no one would say anything about your little wake with this setup.
​

I think you should get your tach checked for accuracy, I find it hard to believe at idle you have that big a wake

smclear, jaxnjil mentioned something interesting, how about adding trim tabs, or flaps, of some sort, (like an airplane),,, Bennet tabs, or maybe even a home built, custom idea that you could drop at idle, and raise up manually, or remotely. I'm sure that would be the cheaper, easier way to do this.​

 

[scipper77]

Re: Large Wake

SMclear,
It's kind of hoaky but if the wake is only a problem in the channel would a drift sock be an option. This post is based on your comments that the boat has no mechanical issues which I take to mean that your wake is supposed to be what you describe.

 

[Scorpion 210 LTD]

Re: Large Wake

The drive does not matter for the most part regarding idle speed. A BBC is a BBC. Set it at 700 RPM-and check your wake then, if it does not stall or bog coming out of the hole (doubtful!! with a BBC in an 18' boat) then you are all set. The previous posters were only noting that there manuals say a lower RPM is acceptable and in their cases desirable. IMO any transmission or power transferring device will last longer and like you better if you shift in at a lower RPM.

 

[oops!]

Re: Large Wake

i boat thru a narrow shallow channel....no wake to me means no wake....not a ripple....so an 8 inch roller ....id be yelling at you too.....

as i run an i/o.....i can only suggest you work the nutral....(in and out of gear)........or a drift sock.......(two big honkin 5 gal buckets dragging behind the boat on a string.

as suggested you could allways make and operate a prop thrust deflector. but that will cost money

 

[RotaryRacer]

Re: Large Wake

mmmm I love Century's.

Green isn't my favorite color, but that is a great boat.

I think the wake is typical for the hull shape and drive system. In my experience it often requires to go into and out of gear as you make your way down the channel.

Don't change your set up. It is correct for the boat.

 

[jaxnjil]

Re: Large Wake



this is a link to the wake we leave. its in the no wake zone in horseshoe canyon on flaming gorge.

 

[abj87]

Re: Large Wake

mmmm I love Century's.

Green isn't my favorite color, but that is a great boat.

I think the wake is typical for the hull shape and drive system. In my experience it often requires to go into and out of gear as you make your way down the channel.

Don't change your set up. It is correct for the boat.

your going to burn up your clutches/put unnecessary wear on the transmission if you bump it in and out of gear constantly. if you have a 1:1 transmission and you lower your idle from 900rpm to 650 in gear you will have reduced your prop rpm 28% which should provide a significant change in your headway speed. You wont hurt anything by running it at 650.

 

[drewmitch44]

Re: Large Wake

Get the prop that will get you to 5,400 rpm at WOT. That is the optimal thing for your motor and that will also get you to slow to a "no wake" speed. Im not sure what kind of prop you got on there now but you need to do it right!