888 Mercruiser, 26' Bayliner

[dklortie]

Hi Guys,
I have a 1979 Bayliner Saratoga 2550 with a Mercruiser 888 power plant that we just bought this spring. After having it out this weekend, I realize that the boat is obviously over pitched on the prop, currently a 19 pitch prop. WOT is about 3100 RPM with the boat trimmed out as best as I could get it. Top speed around the 23 mph range according to the GPS. Looking at the specs in the repair manual, it says I should be around the 4000-4200 RPM range at WOT.

The previous owner had hit with the old prop, and when he went to the marina to get a new one, he told them the engine and boat specs, and just handed him the 19 and told him that is what he needed. The boat is definately struggling with this combination, and having to basically run at or near WOT (3100 rpm) to keep the boat on plane. I have checked the timing, and changed the plugs and wires on the boat. The old plugs were blacker than I had ever seen a set of plugs in my life. I am assuming that it is because the engine is labouring so hard (1000+ rpm lower than spec).

Boat is a 1979 Bayline Saratoga 2550 Hard top (26'). Dry weight is 4800lbs. Add water, fuel, gear and a dinghy on the swim platform, I figure it probably puts me around the 5800lbs range. Currently a 19 pitch 3 blade prop is on the boat. I am wondering if I should go with a 17 pitch 4 blade, or perhaps even a 15 pitch to bring the rpms up closer to spec.

I am burning way too much fuel this way (almost 70 litres for 1 hour of running at 23 mph on flat calm water!!). I believe this is due to the engine labouring so hard. The old 302 that I had in my old boat would use maybe 30-40 litres of fuel in an hour at 3000 rpm.

Any help would be greatly appreciated.

 

[Maclin]

Re: 888 Mercruiser, 26' Bayliner

The engine is lugging also and that will cause problems sooner or later, you are right to bne concerned and I would not run it again until a new prop is acquired.

It is difficult to give a good recommendation without knowing the actual drive ratio. I think it would be 1.6, and with the rpm and mph given that is 33% slip which is a lot.

If I had to pick one I would get a 15 pitch, no higher.

 

[dklortie]

Re: 888 Mercruiser, 26' Bayliner

Hi,
Thanks for the information. From what I could find on the internet, the gear ratio for this outdrive is 1.5. I am not as worried about the top end speed as the fuel economy. I would rather run the engine at 20mph 3200-3400 working efficently, than 22mph at 3000 labouring. As I had stated before, my old boat (length and speed aside...) with the same block burned almost 1/2 the fuel for the same amount of run time at the same rpm.

 

[Bondo]

Re: 888 Mercruiser, 26' Bayliner

Hi,
Thanks for the information. From what I could find on the internet, the gear ratio for this outdrive is 1.5. I am not as worried about the top end speed as the fuel economy. I would rather run the engine at 20mph 3200-3400 working efficently, than 22mph at 3000 labouring. As I had stated before, my old boat (length and speed aside...) with the same block burned almost 1/2 the fuel for the same amount of run time at the same rpm.

Ayuh,.... Welcome Aboard,....

I'd think yer gonna be lookin' at a big ole elephant eared prop, down in the 15", 16" range....

That's Alota tonnage, 'n a little bitty motor....

 

[dklortie]

Re: 888 Mercruiser, 26' Bayliner

Thanks for the information. I was able to find someone who had the original owners manual for the boat, and there is a section on suggested props for the different engine combinations for all of the different models of Bayliner boats that were made in 1979. According to the manual, for a 2550 with the 188hp Mercruiser the suggested prop is a 15 x 15C. That raises another question. I have found someone who has a 15 x 15 prop that I can borrow but it is not the cupped style. The manual advises that engine models with the cupped prop should not run a straight pitched blade. Will I do damage to the engine by trying this prop, or should I just bite the bullet and go out and buy a cupped 15" prop and be done with it?
Regards

 

[steelespike]

Re: 888 Mercruiser, 26' Bayliner

A cupped prop should be more efficient.
As you may know;
any motor needs to be propped so it can rev freely within its rpm band.
It will be more efficient and have better hole shot, throttle response
and easier cruising speed. Need to keep rpm low with the throttle not the prop.

 

[dklortie]

Re: 888 Mercruiser, 26' Bayliner

Hi Guys,
Thanks for all the information. I picked up a 16 x 15 prop and got it on over the weekend. WOW what a difference the right prop makes. Went from 3000rpm wot at 20mph to 3800 rpm wot at 38.6mph. Cruise of 3000 rpm has me doing 27.8mph. Pretty respectable in my books for a 188hp pushing a 5500lb 26' boat. Only thing that I found is that I have to slowly bring it up on plane. Tried to put thet throttle down to see how long it would take to get on plane, and the prop broke free and engine reved out. Thankfully I had my hand on the throttle at the time. (thought I spun the hub). As long as I take my time and slowly increase the throttle to put it up on plane, it runs great. Had the boat out over the weekend, and the same trip as the long weekend which took 70 plus litres of fuel to complete, was only 23 litres when I filled up the boat again. The $100 invenstment in the prop already paid for. Not to mention that the engine sounds much better now. No longer straining so hard to keep going.

Once again, it is great to know that there is the expertise out there and that those with the knowledge are willing to share it with others.

 

[Maclin]

Re: 888 Mercruiser, 26' Bayliner

Good deal!