1979 260 weekender what ratio and prop should i run

[heavyc]

I have a 79 260 weekender with 260 merc alpha 165r gear ratio it has a 15 p aluminum prop have to keep it about 3800 rpm to be cleanly on plane tabs up and trimmed up a bit runs about 22 mph at 3800 wot is 4600 tried a 17p stainless comes out fine but have to keep it about 4000 rpm to stay on plane any ideas I know this boat is heavy but rpm seems a little high bottom is painted and ran with about 60 gal of fuel 2 fat boys on board also engine is fresh boat came with a 305 cracked I replaced it with a 290 hp gm performance parts crate eng.

 

[BillyT0020]

Its your gear ratio that's incorrect. The 5.7L runs a 1.5 gear ratio, I believe the 1.65 is for a V-6. Your numbers are not that far off though. At WOT 4200-4800 (4600 is about perfect) you should be running around 27 mph. Even with the correct gears your going to need around 3800 rpms to maintain a plane. If your getting close to 4600rpm WOT with the 17p SS prop after you get the correct outdrive, I would stay with that.

Design flaw, the boat should have had a Big Block in them from the factory.

On a side note, Im in Dublin but our Boat is on Catawba, where do you take your Weekender?

Good Luck!

 

[heavyc]

I got a chance to try a 16x16 aluminum tuesday and can stay on plane abuot 3500-3600 looks like thats as good as it gets thanks for the input I usually just go to alum creek Moms got a place at east harbor we make it out there sometimes

 

[brains06]

Whoa whoa! I have a 78 dancer with the same motor and I have to disagree with you Billy. I have the 260hp merc 350 and even when it was over-propped with a 17p, it still had better numbers than what you two are posting. I would run 20-23 uphill and 22-25 downhill at about 3400rpms. I dropped to a 15.75x16 and I now run 22-24 uphill and 24-28 downhill at 3400 and I can stay on plane down to 2900 or so maybe less and cruise around 17-20mph. Now Billy you said he should expect 27mph at wide open and I get 36mph at 4400. My first suggestion would be to dump that 17p, they suck for our boats. I couldnt believe how much better my boat ran with the 15.75 cupped prop over that one. Also, I've never used a stainless...if that gives any idication of performance possibilities. Secondly, how are you using your outdrive trim? I've found this makes a huge difference too since our boats are about as long as you can get with a single screw...proper torque usage is a must. I've gotten the best results keeping the trim all the way in to get up and then bumping it out a very little. My boat flattens out and I never have needed my tabs to help me get on plane. I run them full up and then use them when necessary to fight any listing. So those I guess would be my three tips, ditch the 17p, its killin you. Pay attention to trim angle and tab usage. Oh, one last thing, ....maybe two. If you find that you just point to the sky try more throttle and then back off. I normally start at 39-4000 rpms and then back down to 34-35rpms after we get on plane. And also, sometimes, especially going into the wind, I DO use my tabs to help keep the bow down.

Good luck, let us know if this helps.

 

[BillyT0020]

Whoa whoa! I have a 78 dancer with the same motor and I have to disagree with you Billy. I have the 260hp merc 350 and even when it was over-propped with a 17p, it still had better numbers than what you two are posting. I would run 20-23 uphill and 22-25 downhill at about 3400rpms. I dropped to a 15.75x16 and I now run 22-24 uphill and 24-28 downhill at 3400 and I can stay on plane down to 2900 or so maybe less and cruise around 17-20mph. Now Billy you said he should expect 27mph at wide open and I get 36mph at 4400. My first suggestion would be to dump that 17p, they suck for our boats. I couldnt believe how much better my boat ran with the 15.75 cupped prop over that one. Also, I've never used a stainless...if that gives any idication of performance possibilities. Secondly, how are you using your outdrive trim? I've found this makes a huge difference too since our boats are about as long as you can get with a single screw...proper torque usage is a must. I've gotten the best results keeping the trim all the way in to get up and then bumping it out a very little. My boat flattens out and I never have needed my tabs to help me get on plane. I run them full up and then use them when necessary to fight any listing. So those I guess would be my three tips, ditch the 17p, its killin you. Pay attention to trim angle and tab usage. Oh, one last thing, ....maybe two. If you find that you just point to the sky try more throttle and then back off. I normally start at 39-4000 rpms and then back down to 34-35rpms after we get on plane. And also, sometimes, especially going into the wind, I DO use my tabs to help keep the bow down.

Good luck, let us know if this helps.

Thanks for the input I will definitely have to try one of those props if your getting numbers like that!

I was out this weekend with 5 people onboard, about 50 gallons of gas, 25 gals of water in pretty good chop at first and then very smooth and couldn't get the boat over 24 mph (verified through GPS) at 4400 rpms which is WOT for that prop. It did seem better then when I had the 14.5 x 15 Vengeance with only 2 people though. I think the surface area of the prop may be too small and not pushing enough water for that big of boat.

Although others have said the Merc Vengeance 15 (really a 14.5) x 17p was the best prop for the boat.

So your using a 15.75 x 16p cupped prop? If its cupped wouldn't it make it 15.75 x 17? I have always been told that a cupped prop adds about 1 in of pitch. I wonder how you are getting that high of RPM's at WOT because it should be lower then my 14.5 x 17 if its actually closer to a 15.75 x 17.

Any reccommendations as to which prop to go with manufacturer wise? A model number would be awesome! As cheap as aluminum props are I'll buy one just for comparrison!

Thanks!

 

[jons79searay]

Here is my non-expert .02 cents.

You said that you never used a stainless prop. From what I have read and
heard is that the blades do not flex near as much and gives a better push
or thrust. Aluminum blades really flex trying to push that big of a boat on a
single prop. It should make a big difference. The harder steel bites and pushes
better especially for heavier boats like ours. Remember, when your prop flexes
it changes the pitch.

Also, I agree with the 1.50 ratio outdrive. I would use the 1.5 ratio for the 5.7L/V-8.
and use the 1.68 for the 5.0L/V-8

 

[BillyT0020]

Here is my non-expert .02 cents.

You said that you never used a stainless prop. From what I have read and
heard is that the blades do not flex near as much and gives a better push
or thrust. Aluminum blades really flex trying to push that big of a boat on a
single prop. It should make a big difference. The harder steel bites and pushes
better especially for heavier boats like ours. Remember, when your prop flexes
it changes the pitch.

Also, I agree with the 1.50 ratio outdrive. I would use the 1.5 ratio for the 5.7L/V-8.
and use the 1.68 for the 5.0L/V-8

Jon,
I have always heard the same thing but I am getting tired of buying SS props playing around with pitch and diameter to find the best suited for my boat. I may just try an aluminum to see if a 16 x 16 is the way to go. Part of my problem may have been the tabs, I was using full tabs with the 14.5 x 17p SS in order to get on a plane and keep the nose down. The other part of the problem is probably me not trimming up the drive when I get up on a plane. I also think that the 14.5 diameter is probably too small, everything I have seen recommended a minimum of 15.5 diameter with some all the way up to 16. I may end up selling both my vengeance props and getting a 15.5 x 15 mirage plus.

What kind of numbers are you getting with your prop? What prop are you running?

Thanks,

 

[Tail Chaser 661]

Way too much effort figuring all this stuff out. :smt101
Just put in a bigger engine :grin::lol::lol::lol:


Dont know the exact Dia.
Got 22 kts at 3500rpm and 28 kts at 4000 rpm with a old Quicksilver Stainless 17" pitch. GPS Speedo
A bit overproped, But the 22 kt cruise works for now.

heavyc
His 1.68 GR will put more TQ to the prop.
The gears are a little weaker due to more thinner teeth then the 1.5 ratio drive.
He is able to spin the 16 x16 Alum prop because of the 1.68 ratio.
I did not like my 16D x 14p Alum with my 1.47 ratio.
I doubt I could push a 16 x 16 prop. Was tempted to try.
My repower will have 2.2 ratio 15.5"D x 26"P duoprop.
Now were moving right along :grin:

Hey Billy,
My trim gauge does not work. But......
I trim my drive all the way in, Then I give a quick double tap outward on the drive.
My digital intastrim gauge I run two lights in the bow down position. 20% Down? On the trim tabs.
At 18 to 20 mph. I go 0% or 10% on the trim. Then watch GPS speedo to see if I lose MPH. Re adjust if necessary
Any more then 20% of trimtab creates a lot of drag.

I plane OK at 18mph, pretty good at 20mph. Boat runs bitchin above 23mph

 

[BillyT0020]

Tail,
That probably explains a lot of my low speed at WOT. I know I was running way more the 20% tabs, prob closer to 75%. I hate that feeling of the bow to the sky and instantly start hitting tabs if she doesn't start coming down pretty fast. Plus I havn't been kicking my drive down at all. And I had 5 people onboard. Not sure if all that adds up to 13 mph for a top speed of 36 at WOT of 4400 with the SS 17p. If its calmer out this weekend I'll get her out with just the admiral and I and run no tabs and trim the drive out and see what kind of numbers I get. I do know that the 14.5 x 15P SS Vengeance seemed way under propped because I was getting a WOT of 4900 which is 300 rpms more then the max 4600 Merc Recommended for the 260. It did seem to plane out easier but seemed even slower then the 23 mph I got this weekend. And that was with only 2 people but I didn't have the GPS with me to check mph. If its not the prop not sure what else it could be as I have over 150 psi in all cylindars, a new ignition system, its timed correctly, the drive is rebuilt, new fuel tank and hoses/filters. Carb does probably need to be rebuilt this year but doubt that has anything to do with it.

Anyway guess Ill have to do some more test this weekend with both SS props and maybe a 16 x 16 aluminum if I can find one before the weekend.

P.S. The 454 MAG I'll be picking up this weekend wont be rebuilt for awhile so I'll have to figure out this setup for the next couple of seasons!

 

[Tail Chaser 661]

I'm very easy on the throttle during take off.
With the drive all the way in. I noticed a little stern lift.
Near 10 MPH, Its starts pushing the bow down causing some drag.
Then I make sure im at the double tap outward position on the drive. Then play around with one or two lights on the bow down position. Two lights 20%? work best 80% of the time at speeds up to 18 mph. Then I try one light 10% or 0% trim to eliminate drag.

Sometimes I screw up, I notice the boats running awful.
I have the trim tab at 4 lights bow down position 40%?

Are your plugs burning nice and Tan Color?
Years ago, Having the OEM oversized Quadra junk carb.
Boat was just bogging down. Second time out with that condition my float stuck.

I put on a 600 cfm Edelbrock marine carb. Problem solved.
A scary thought, But maybe weigh your boat.
If its waterlogged, Could be very heavy :wow:

Also make sure your drive is going all the way down.
I noticed mine stopped short a couple of times while on the trl. Hopefully looking at the angle. The prop thrust will be pushing upward on the stern a few degrees. Then a double tap outward on the drive is pushing you straight.
U joints like that position also.

 

[BillyT0020]

I'm very easy on the throttle during take off.
With the drive all the way in. I noticed a little stern lift.
Near 10 MPH, Its starts pushing the bow down causing some drag.
Then I make sure im at the double tap outward position on the drive. Then play around with one or two lights on the bow down position. Two lights 20%? work best 80% of the time at speeds up to 18 mph. Then I try one light 10% or 0% trim to eliminate drag.

Sometimes I screw up, I notice the boats running awful.
I have the trim tab at 4 lights bow down position 40%?

Are your plugs burning nice and Tan Color?
Years ago, Having the OEM oversized Quadra junk carb.
Boat was just bogging down. Second time out with that condition my float stuck.

I put on a 600 cfm Edelbrock marine carb. Problem solved.
A scary thought, But maybe weigh your boat.
If its waterlogged, Could be very heavy :wow:

Also make sure your drive is going all the way down.
I noticed mine stopped short a couple of times while on the trl. Hopefully looking at the angle. The prop thrust will be pushing upward on the stern a few degrees. Then a double tap outward on the drive is pushing you straight.
U joints like that position also.

Plugs are new, not sure if they are tan or not, I guess if not Ill have to mess with the mixture screws but I don't have a tach guage that will measure that precise. I doubt the boat is water logged, it sits fine in the water, no sagging whatsoever. Plus if there is foam in our boat i'm not sure where they would have put it. Seems to me like its mostly fiberglass but its slipped so I will have to wait until winter when its pulled to try and weigh it.

I may end up buying a new carb for next season, but would rather put them money into rebuilding my 454 MAG, but also want to get atleast this and next season out of the 260.

I don't have trim tab indicator lights on my setup so im not sure how much tabs I was running but it very well could have been almost all the way down. I also was not playing with the drive. Weather permiting at the lake this weekend, I think what Im going to is keep the 17 p prop on and run it out with no tabs regardless of how high the bow is, kick the drive out until the bow starts to pulsate then back in a hair, and see what kind of numbers I get with 2 people at WOT. If they still super slow at 4400 I will put the 15p prop back on and see how it does with that one. Have to be carefull to stay under 4600 rpms with that prob because last time at WOT it was running at 4900. If all is still not right Ill try a larger diamter aluminum prop like the 16 x 16 thats been recommended.

I am still curious as to why you are getting only 4000 rpms at WOT with your 17p prop Tail. Seems like you should be getting atleast 4200. Hell if I can get a WOT speet of 36 mph as others have said they can get with our boat and the Merc 260 I can take my time building the 454 because thats plenty for me.

 

[Tail Chaser 661]

I may be only getting 4000 rpm because....
I installed a fuel flow gauge last year.
Turns out my throttle control is hitting it near full throttle.
The test was also done in the ocean with a 2' swell.
Also my bimini catchs a lot of air.
I also have atleast one tired cyl.

I was also overdue on a tuneup and filter. Wanted a shakedown run first. Deciding on repower or wait.
I haven't checked compression for three years.
Most cyls above 150psi, But had one down at 118psi it went up to 125 after squirting oil in the cyl.

Same prop, turned 4200 rpm in light whitecap 5 yrs ago.

Ajusting your carb.
FOCUS and count the # of turns your mixture screws are out.
Nothing worse then not being happy with an adjustment you made, And then not knowing the ORIG setting.
Around 1 1/2 turns out is normal factory specs for almost all engines. A safe starting point.

# 1 I usually turn the screw IN very slowly till the engine just starts to stumble Then maybe 1/4 to 1/2 turn back out on the screw from there. looking for highest smoothest idle
#2 Some books say between the stumble turning in and where it starts getting rough turning back out. I check that out of curiosity. Because that's the middle of the lean/rich setting
#3 With a Vacuum gauge attached to the intake or vacuum source on carb. Books say, Go for highest vacume setting.

Always good to check the plugs on such hard driven engines.
You dont want to melt a piston, And its nice to know the fuel is being burned getting good power out of all the cyls.

I was admiring the exhaust color on my 496ci exhaust risers yesterday. Maybe a tad rich, But its not going to cook the internals.
I dont understand why your boat rides so bow high :huh:
Maybe you could tie a few Fat girls down on your bow pulpit:lol:

 

[Tail Chaser 661]

Another important note.
Theres more then only pitch and Dia of how a prop performs.
Theres the blade area (MASS) and other stuff.
Thats what really sucks. Looking at only the Dia/Pitch is only part of the equation

My Alum 16 x 14 Alum has huge blades.
My three stainless have fairly small blades.
A prop guy told me Mercury stainless props suck.
The Tech guys come up with a good design.
Then the accountants have them retooled for a cheaper production prop :huh:

He did not recommend me a prop mfg:smt013
He did say there a cheaper props that work much better then Mercs.

He did say the Merc Alums, Think its there black diamonds Not the XP. (too much surface area)are a very good props.
Its the model that comes in 16 x 14 and 16 x 16. But not the XP version

Looks like you have it whipped billy
16 x16 alum.
Could get it trimmed down to 15.75 like brains06 if needed.
Maybe check what MFG his prop is
Hire some chubby girls to sit on your bow. Your good to go:thumbsup:

 

[BillyT0020]

Well we'll see how it goes this weekend......

Yeah both Merc SS Props I have look like the blades are really small. Who knows...

Do I have to look at the fat chicks hanging from my bow pulpit?:smt100

 

[Tail Chaser 661]

Do I have to look at the fat chicks hanging from my bow pulpit?:smt100

Looks like your blue tarp could cover most of them up :wow:

 

[DuelingProps]

Hey I'm a new member who got a similar boat last season. and I'm trying to get it running alittle faster.
It is a 79 260 weekender with a 5.7 mercruiser with trim tabs in great condition a lake boat.
It came with two stainless props one is a 14.25"dia x17 pitch with this prop it will only spin about 3200rpm at 21mph if my gauges are accurate.
how fast should I expect this boat to run with the correct prop. is asking for a cruising speed of 30 too much to ask for?

the other prop I'm unsure of it size. but will find out later this afternoon when we pull the boat out.

 

[brains06]

Another important note.
Theres more then only pitch and Dia of how a prop performs.
Theres the blade area (MASS) and other stuff.
Thats what really sucks. Looking at only the Dia/Pitch is only part of the equation

My Alum 16 x 14 Alum has huge blades.
My three stainless have fairly small blades.
A prop guy told me Mercury stainless props suck.
The Tech guys come up with a good design.
Then the accountants have them retooled for a cheaper production prop :huh:

He did not recommend me a prop mfg:smt013
He did say there a cheaper props that work much better then Mercs.

He did say the Merc Alums, Think its there black diamonds Not the XP. (too much surface area)are a very good props.
Its the model that comes in 16 x 14 and 16 x 16. But not the XP version

Looks like you have it whipped billy
16 x16 alum.
Could get it trimmed down to 15.75 like brains06 if needed.
Maybe check what MFG his prop is
Hire some chubby girls to sit on your bow. Your good to go:thumbsup:

Ok, I just got off the phone with my marina so that I could be sure. My prop is a Mercury BlackMax 15 1/4 x 15 and I belive its the cupped version. As I mentioned before, I started with a 17p that was the spare prop to the person I got the boat from. He used it to sea trial the boat for me cuz the good prop got stolen. I could tell the motor was running fine but the boat performed like ****. I almost didnt buy it due to this but the owner jumped up and down swearing that it was the prop. It was! I got right around 4000rpms at WOT so I stepped down to a 16 x 16 and got to 4200. The boat ran worlds better and my hole shot was nice. The Sea Ray prop guide recommends 15 1/4 x 15 so I got one of those and whoa again! 4500 @ WOT and 36mph. I bet if I ran a stainless I could get a few more mph but I like to beach at an island and heaven forbid I bounce bottom with a stainless and a 31 year old outdrive. So $116.00 and I'm good to go.

A word on the use of tabs and trim. I had been overusing my tabs last season and as others have said, it resulted in alot of drag which = fuel. I'm still working out the kinks but for the most part I keep my tabs in full up and the trim full in until I get on plane then I bump it out a bit. I'm gonna give the "two stabs" a try my next time cuz I dont have a trim guage either.

Billy: Our boats arent like the smaller cuddy cabin boats where you can trim out till it starts to porpoise and then bring it back in to find the best spot. We are way too long for that. The key is to place the trim at a flat angle or perpindicular with the water. Out too far and you drive the bow up, not far enough and you drag it in the water. I've found and heard that the best placement for express cruisers our size and larger is not too far from all the way in. If you get a chance, the best thing you can do is to hop in the water and see for yourself where "x" seconds or "x" number of button presses takes the drive and then work it as so.
When you go out this weekend to try some new tactics, put the tabs all the way up (this should take no more than 6 seconds from full down to full up) and when you go to plane, take the r's up to 4000 and let the boat get fully on plane. It may take a moment but if you swinging the right prop it should only take about 6-9 seconds. Then back it down to 3500 and do your speed testing going into and against the current (if there is one where you boat). In the Detroit River we have about a 4mph current on average and it shows up on your gps.

Tail: What has that fuel flow meter shown you so far? I'm thinkin about getting one

 

[brains06]

Hey I'm a new member who got a similar boat last season. and I'm trying to get it running alittle faster.
It is a 79 260 weekender with a 5.7 mercruiser with trim tabs in great condition a lake boat.
It came with two stainless props one is a 14.25"dia x17 pitch with this prop it will only spin about 3200rpm at 21mph if my gauges are accurate.
how fast should I expect this boat to run with the correct prop. is asking for a cruising speed of 30 too much to ask for?

the other prop I'm unsure of it size. but will find out later this afternoon when we pull the boat out.

Dueling: Yeah...wanting a cruise speed of 30 is asking a bit much of a single screw older boat. Now that being said, I'm referring to an economical cruise speed at 32-3500 rpms. In the river I run roughly 24-28 at 3500 going with the current and 22-25 against. I could run at 3900-4000 rpms and cruise at 30 mph but I think I would be burning around 15 gph or so while at 3500 I would be around 10. Read my previous posts in this thread for some prop size suggestions.

 

[Tail Chaser 661]

brains06,
Thanks for the info,
Ive got a very tired engine.
5cyl@125psi, 1 cyl@90psi 1@130psi and 1@150psi
Guess sea water made for bad lubrication 2 years ago.(Leaky Riser) It just did it again.:smt013
My boat came with 3 stainless props when I bought it. All wrong.
Bought a 16 X 14 ALUM after a prop guy said our boats need as big DIA as we can get. Running a 14" pitch sucked.
The 16 X16 Alum is cheap. I know I would have been happy with that, If I could spin it.

That Norstar fuel flow gauge is nice. Cheapest of the bunch.
Last trip out was the first time I used it.
I was burning 13.5 GPH to 14.5 GPH at 22 kts 3500rpm.
2' swell at sea.
I believe I was still showing 13 GPH at 2800/3000rpm below 18 kts. Engine was probably working not being on plane. Was plowing through some whitecap also.

Dueling Props,

You need 500 ft lbs of tq to cruise our heavy boats at 30 mph within a reasonable RPM. A brand new 5.7 260 hp only has 350 lbs tq. Merc 350 Mags only have 355 tq. All the hype of more powerfull EFI engines. Your getitng more HP. (A higher RPM engine) But that does not add much to the TQ of the engines. It takes Torque to get a heavy boat moving. Otherwise I would power my boat with a 13000 rpm chain saw engine. Sounds fast doesnt it :lol: Should cruise 50 mph at 11000 rpm. O'h darn, No tq to get me moving :huh:
The Merc 8.1 Mag with 509 tq at 3200 rpm should do 30 mph at 3000 rpm burning around 12 GPH.
A duoprop gets you a 3 mph increase in cruise speed for the same rpm as a single prop.
So maybe, a 5000 rpm 350 mag with a duoprop may cruise at 30 mph at 4000 rpm. Still kind of high in the rpm range.
There lots of newer 26' Sea Rays that just flat out suck with a small block engine.
26 mph at 3600/3800 rpm seems to be the norm for newer 26' Sundancers with a small block 5.7

 

[rob83srv225]

Here's my 2 cent's. I have a 225 cc with a merc 260, that also came with a 17 pitch alum. prop. The boat ran like crap!!! switch to a stainless 15.25 x 15 pitch, made a world of diffrence!!!! boat jumps on plane, wot is 4400 rpm, and she'll run 39 mph of of the gps w/ 2 people on board and 50 gallons of gas!!!

Robert.