85 26ft Sundancer Prop Help

[Jsnap]

First i want to say High to all and appologize for asking a Question thats prob been asked a bunch of times. I just got this boat and those of you that have it know this is a heavy SOB and in my opinion way underpowerd to have a single SM block In it that being said and being an engine builder i went to work on the motor having an alpha i wanted to keep the HP at around 300. I ended up with with 287 hp on the engine Dyno. My job is done know i neeed you guys to help me with the prop i local marine mechanic i do machine work for gave me these options here goes.
15x15 1/4 searays pick
14 1/2 x 21
14 1/4x19

Now I want you guys that have the boat and did all the trial and error to tell me what to buy thanks all in advance .Richie

 

[WTP07]

This is going to be near impossible to do, as we do not have that kind of power in ours...I don't in mine anyway.

I have the stock "260" HP SB, and use a 4 blade 14.25 x 15P. This tops me out at about 4400 RPM. A little low, but acceptable to me, for what I want it to do. I could probably drop one more pitch and get those last couple hun RPM.

You have 287 on the dyno, so a bit more than me, probably a lot more since yours was a REAL HP reading rather than a manufacturers best guess based on testing 20+ years ago.

I am guessing you could go with a 4 blade 14.25x19P or even 21P and still get to around 4600 RPM.

Keep in mind you are still running an Alpha1, with the extra ponies I'd be hesitant about pinning it off of the starts...

Get a SS prop if you want the best performance.

If you can get to know a local prop dealer, let him know what your plans are and most of the time they will let you exchange props until you get the right one.

Good luck and let us know how you make out!

:thumbsup:


Randy.

 

[26sxl]

A 19 maybe a 21 to much...

 

[BillyT0020]

Its not the HP thats going to affect the prop size/pitch, its the torque. What was the torque peak on your dyno? Find out approximately what the torque of your old engine was from the factory and figure out the difference. For every 50 ft of torque you can increase your prop pitch 2". If your new engine has 100 ft of torque more then stock then try the 15 x 19 and see what kind of RPM's your getting at WOT and adjust as neccesary. Regardless its probably going to be a trial and error process.

Good Luck!

 

[Mooner]

JSnap,
Well here's my .02 worth, and in today's economy, it's worth even less... I just became a proud owner of a 1986 Weekender 268. It has the Mercruiser 260 with Alpha I and it has a 16" X 16 prop. I bought the boat from the original owner, who had done quite a bit of experimenting with different props and he found this one to work best. The boat really gets up on plane rather easily, and WOT pins it at 4200 RPM. I must say, the boat runs superbly and I couldn't be happier at this point. I imagine that my boat is very similar to your 26 ft.Sundancer, as far as weight and hull type.
Keep us posted on your progress.
Mooner

 

[BarryCF]

Echo on the post regarding torque. As I recall, the 260 had 350 ft/lbs peak torque, and the 260 hp rating was pretty accurate. The additional hp is about 10% and I would bet doesn't translate into 10% more torque. I would guess about 20-25 more ft/lbs torque, so maybe another inch of pitch.

 

[CaptainH]

I use the 15.25X15 and am able to run in what I consider an acceptable performance range for the boat. The 268DA is a heavy load to push with the motor/drive you have and looking for more performance may be hard to achive. Having said that I had a great deal of improvement when I installed a new prop as the one on the boat when I bought it was a bit worn. Previous owner went clam digging a few times. I stayed with aluminum on advice of marina mechanic due to if there was an impact the aluminum prop is $200 and a drive unit is $3000. Also the extra weight on the boat, amount of gas, water, beer, passengers, etc. will have a significant effect on performance as well.
By the way add your boat info and location to the signiture line. Welcome aboard.

 

[Mooner]

Captain H,

You made me laugh. You listed factors in how much weight is being carried onboard....gas, water, passengers, and BEER!. Yikes! Let me know when you're having a boat party and I'll be there, plenty thirsty, I assure you. lol :thumbsup:
BTW....nice boat!

 

[brains06]

JSnap,
Well here's my .02 worth, and in today's economy, it's worth even less... I just became a proud owner of a 1986 Weekender 268. It has the Mercruiser 260 with Alpha I and it has a 16" X 16 prop. I bought the boat from the original owner, who had done quite a bit of experimenting with different props and he found this one to work best. The boat really gets up on plane rather easily, and WOT pins it at 4200 RPM. I must say, the boat runs superbly and I couldn't be happier at this point. I imagine that my boat is very similar to your 26 ft.Sundancer, as far as weight and hull type.
Keep us posted on your progress.
Mooner

I'll bet you 2 dollars that if you tried a 15.25x15 you'd be even happier. I had the same prop/engine combo in an even heavier boat and the 16x16 was great (and is still my spare) but the 15.25x15 is perfect. I spin 4400 and run nice and smooth. Gets up fine with plenty of people....and beer!

 

[CaptainH]

Captain H,

You made me laugh. You listed factors in how much weight is being carried onboard....gas, water, passengers, and BEER!. Yikes! Let me know when you're having a boat party and I'll be there, plenty thirsty, I assure you. lol :thumbsup:
BTW....nice boat!

Even with what I also consider is an underpowered engine/drive for the 268DA I can still get on plane in a short run and cruise at an acceptable speed. Other boat owning passengers I have had on board commented on the good performance as well.
Mooner,
Well you have to keep the boat well stocked for guests!
I have to ask about your handle, is there a story behind it? A few years ago I was in a Roman Gabrial golf tournament in Myrtle Beach and my foursome mooned the group behind us as they were teeing off. The funny part was the applause we got from the homeowners beside the fairway that were outside on their patios watching us. If you ever get to the beautiful SC coast let me know and maybe we can quench that thirst of yours.

 

[Mooner]

Capt. H...
Thanks for the prop info. I have an extra prop, but I'll need to check it again to see what configuration it has.
My nickname was earned while at The Ohio State University. I'll just say....the girls dorm was next to ours. I felt obligated to keep them happy.
Hopefully, I'll get to the boat tomorrow. The weather is supposed to be quite nice. We;'ll go for a cruise on Lake Erie, drown some minnows on perch, then come back to the marina and relax with some refreshment on the boat, maybe drop a line there too.
I'll have a sip or two for you too....lol
Mooner

 

[Tail Chaser 661]

There was a recent big O'L boy with two big friends having prop issues. He was happy with the 16 x 16 Alum.

I think brains06 was using a cupped prop that he liked so much :smt017

 

[eddiezuskin]

I was just looking at Searay website WRT props as mine has gotten rather beat up and I want to replace. Searay says 15.25 x 15 for all its SB 260hp with Alpha 1, BB got 14 x 19.
My 1987 250DA got its best performance when this prop was new, 32mph at 4400rpms. I bought it for $50 in a Boat Us Clearance bin because it was 15.25 x 15. My mechanic says it has odd shaped blades and that I might do a bit better with standard looking ones. He, also, suggested trying a 16 x 16. For last 2 seasons I sent my $50 prop to be reconditioned for $75. I think its time to replce it and keep it for a spare.

Eddie

 

[brains06]

There was a recent big O'L boy with two big friends having prop issues. He was happy with the 16 x 16 Alum.

I think brains06 was using a cupped prop that he liked so much :smt017

I do, I have the 16 x 16 and it was worlds better than the 17p I had when I got the boat but the 15 x 15.25 or whatever is the best of both worlds. My mileage is good and my speed is good too, WOT @ 4400 is 36-37mph and my boat is a 78 with the thick fiberglass. I was thinking about swapping out this weekend just to record the differences. We'll see though.

 

[Tail Chaser 661]

I do, I have the 16 x 16 and it was worlds better than the 17p I had when I got the boat but the 15 x 15.25 or whatever is the best of both worlds. My mileage is good and my speed is good too, WOT @ 4400 is 36-37mph and my boat is a 78 with the thick fiberglass. I was thinking about swapping out this weekend just to record the differences. We'll see though.

I'm looking forward to trying out the Cupped 26"P x 15.25"D duoprop with my new engine :grin:
I should be 30 mph @ 3000rpm and 35mph @ 3500rpm
Wishful thinking is WOT @ 50 mph
Time will tell.

 

[brains06]

I'm looking forward to trying out the Cupped 26"P x 15.25"D duoprop with my new engine :grin:
I should be 30 mph @ 3000rpm and 35mph @ 3500rpm
Wishful thinking is WOT @ 50 mph
Time will tell.

are you gonna have to use a shoehorn to get that 8.1 in? I'd love to hear/see that finished product. Is there a major weight difference in the two motors?

 

[BillyT0020]

I'm looking forward to trying out the Cupped 26"P x 15.25"D duoprop with my new engine :grin:
I should be 30 mph @ 3000rpm and 35mph @ 3500rpm
Wishful thinking is WOT @ 50 mph
Time will tell.

That Picture Sure Looks Like your swapping engines out sooner then expected Tail! You decide to do it now?

 

[Tail Chaser 661]

brains06
A couple of hundred pounds more.
Installs going to be a bitch. Was planing some fuel tank mods. Trim the tank 4". The stock tank looks like the 8.1 needs 1/4" more room.
The engine coupler on the 8.1 is the same as the diesel.
The spline shaft that accepts the drive sticks out about 4 inches. A stronger setup for the massive TQ these engines put out. All other couplers are flat.
The 8.1 is 3" longer. Then you got that coupler shaft sticking out about 4" Need to clear the inner transom plate with that.
Wishful thinking a Bravo inner transom give a little more working room.

Worst scenario may have to use a normal flat SB/BB coupler.
Going through the hassle of upgrading to a Bravo drive.
I'm glad I will be pushing much more power then a Alpha could ever handle.
Otherwise looks like a 383ci with 16 x 16 prop with the Alpha would have been the easy route.
Dont think I would have been comfortable heading 100 miles straight out to sea with that. Probably out of radio range for any help also.

 

[Tail Chaser 661]

That Picture Sure Looks Like your swapping engines out sooner then expected Tail! You decide to do it now?

Yep!... Having a rocker arm laying on its side in the valve cover on the 5.7 gave me the motivation.:lol:
A complete tuneup and two oil changes after that little water intrusion incident. Trying to maybe get another season out of the old 5.7 did not happen.
Looking forward to putting some big power behind my boat now.:grin:

 

[BillyT0020]

Thats awesome man! I know you were working though some gas tank issues but when do you think you will have it ready to splash?