Advice on new SS prop please

[michalakmj]

I bought my dad's old boat, the one that's been in the family since 1988, and am now giving some needed TLC and addressing some issues that I feel have been overlooked. The boat was repowered in 1997 and in my opinion it was never quite the same after that- the boat mechanic who did the swap did several "tune-ups" to correct it but my dad was never quite satisfied and in the end I think he left it "good enough". I've rebuilt the carb, properly re-timed the engine and adjusted the mixture, new igniton components, engine runs great now. It is now time to address the prop and I feel after reading numerous threads in the archives that the fellows on this forum will be better able to help me that my local marina.

Iboats Boat and Motor Info

1. Year, make and model of boat
- 1985 Century Fiero

2. Length, width and base weight of boat, look for boat decal on back of boat
- 22.5' x 8' 2300 lbs.

3. Number of people and gallons of gas normally on boat
- 3-5 people, 42 gal

4. What do you use the boat for
- Skiing and cruising

5. Is it a Deep Vee and if so how many degrees of deadrise
- Not a true deep vee, I believe it's called a modified vee or medium vee. I can possibly measure the angle this weekend if it'll help.

6. Year, make and model of motor
- Repowered with a 1995 Mercruiser 5.7 with Rochester 4 barrel and Thunderbolt V ignition

7. HP and gear ratio of motor IMPORTANT
- 260 or 265HP, gear ratio 1.47:1

8. Manufacturer?s recommended WOT range
- 4200-4800 RPM

9. Anti-ventilation Plate height above keel of boat if it is an outboard in inches
-N/A

10. Is it a bass boat or does it have a pad bottom
-N/A

11. Does it have a hydrafoil or trim tabs
- no

12. Make, model, diameter, pitch and whether SS or aluminum prop
- Currently running a 14" 17p Merc SS prop. Don't know the model, it's at least 15 years old. I don't know how to read the prop numbers exactly, so not sure if it's true 14" or 14.5", etc. 3 blades, each blade has some rough edges. Originally had a 14x19 SS (as per boat manual) before repower; after repower engine was overrevving so my dad switched to the 17p.

13. WOT RPM and speed from prop, how much gas and how many people in boat for test data
- I did two tests and here are the results:
- 3 people, 30 gallons: 4800 RPM, 45mph GPS, acceptable holeshot
- 5 people, 30 gallons: 4200 RPM, 43mph GPS, bad holeshot

14. What problems are you trying to cure or what are you looking for the boat to do that it is not doing the way you think it should or to your expectations
- First the boat is a bit of a dog coming out of the hole with 5+ people, which makes it a drag to pull skiers. I weigh 225 and use a slalom, and have a hard time getting up because the boat planes slowly. If I'm skiing with 2 people on the boat it's way easier. Before the repower my dad used to ski slalom at 220 lbs and we had no problems pulling him up with a boatload of people.
- I'd like to understand why my WOT goes from 4800 with 3 people to 4200 with 5 people. Is this a true effect, or is it more likely my tach is going bad?
- I'm fine with the top speed. Of course if I can go faster I'd like that, but my main concern is to improve the boat's acceleration without reducing the top speed. I know the prop is lightly damaged, but I figure instead of paying for a repair I'd be better off looking at a new model with the possibility of improving my performance.

Any help you can provide would be appreciated. If you need any pictures posted of the hull or the current prop, I can get them and post them on Thursday.

Thanks,
Mark

 

[fossill]

Re: Advice on new SS prop please

What kind of engine did the boat originally have before repowering?

 

[michalakmj]

Re: Advice on new SS prop please

Sorry, it had a 1985 Mercruiser 260. Same 350ci 260HP engine basically before Merc started calling it the 5.7. The '95 5.7 it has now came out of a wrecked '95 boat with a Bravo One drive.

 

[countvlad]

Re: Advice on new SS prop please

the reason why the rpms drop with more people is because there's more weight... its normal... nothing to worry about...

for a better hole shot you can purchase a 4 blade prop... but unfortunately you are probably going to lose some top end.... i cant sugest which prop to get because im not very familiar with 4 blade... good luck

 

[michalakmj]

Re: Advice on new SS prop please

I have an aluminum 14x19 spare that I keep in the boat- I'm going to throw it on this weekend just to see what it does. I used the Merc prop finder app and it basically said to stay in the 17-18p range. My boating partner found some prop app on another website that actually listed our make and model boat, and he said the website recommended a 21 pitch for skiing and 23 pitch for top speed. That doesn't make a whole lot of sense to me.

I'm not opposed to keeping the SS prop I have now and finding an aluminum prop to swap out for skiing when I know I'm going to have more than a few people on board.