1988 100HP mercury ELPTO max rpm/prop recommendation

[SeaRay Seville]

In serious need of some help! Just bought and took my Sea Ray Seville 160 BR out with an 88 100hp mercury 4cyl. boats weighs 1530lbs dry and had a full 20 gallon tank, cooler, 2 batteries and 45lb anchor and it did 97% ok. My questions: the factory tach showed 5900-6000 if I got the trim just right and it maxed out at 43mph and 42.9mph on 2 gps units. The hole shot was a little slower than my 79 Lund Sirius 15ft 750lb dry weight, 5gal gas, 1 battery. with an 85hp mercury from 78 this boat hit 39 and 39.5mph on same gps units Prop on the Sea Ray is a ballistic 3 blade 13.5x17P would adding a hydrofoil help get my planes quicker? I have no info on prop of Lund or rpm but it's been an awesome boat. Bought the Sea Ray for room/comfort. Any help/info would be greatly appreciated! Basic question is can I get the Sea Ray outa the hole quicker without sacrificing much (or any) top end and is 6000rpm too much (if that's accurate on the tach ordered a new test tach already)

 

[jimmbo]

Your engines rpm range is 4750 - 5250. It was recommended not to exceed the upper limit on those engines. That might be that if run faster the engine will be far enough past peak torque to have a substantial reduction in hp
Hydrofoils... trashcan filler in my opinion.

 

[SeaRay Seville]

I appreciate the info, all I could find for rpm was 5200-5700 depending who said it. It keeps climbing in top speed with trim adjustments until the factory 1988 tach says 5900-6000 so it's not losing HP, tach may be off its old. I'll see on Friday with the new one. I'm not to thrilled with the idea of a hydrofoil either. Any recommendations for a better hole shot without over revving?

 

[ondarvr]

That's not what foils are designed to do, but the marketing department will tell you it is. Trim tabs will help a great deal and aren't that expensive.

 

[SeaRay Seville]

Where do you get the specific trim tabs and what are hydrofoils for, just to prevent bow bouncing at speed?

 

[SeaRay Seville]

Ok just googled trim tabs (didn't know that's what they were called) how the heck does that effect planing out?

 

[ondarvr]

There are many brands styles and sizes of trim tabs, but they aren't specific to a hull or brand, you just buy the type you want or need. Explaining what a foil actually does typically leads to lengthy and emotional "discussions", so I'll just leave it be.

 

[SeaRay Seville]

So I'm a bit confused, by trim tabs do you mean the ones that mount to the rear of the hull or the little anode "trim" tab just above the prop? Excuse my ignorance we all start somewhere!

 

[ondarvr]

Trim Tabs mount on the hull.

 

[SeaRay Seville]

More on topic, if I switched to a 14"x17P prop or a 14"x15P would I gain a better hole shot with either? Less/more rpm? Better/worse top speed?

 

[ondarvr]

Better hole shot with less pitch, going up in pitch will lower your RPMs. As for top speed, you need to test with good tach and a GPS to dial it in for the correct RPMs

 

[jimmbo]

Drilling vents in the prop may help the hole shot

 

[SeaRay Seville]

Where would you drill the holes, do shops do this? So changing the pitch up/down I get but switching from 13.5" to 14" wouldn't that effect rpm/hole shot/top speed as much as pitch? Tach should be here Friday but it's really cold up here again probably be 2 weeks before I can hit the water.

 

[ondarvr]

Diameter isn't going make a big difference

As you go down in pitch diameter typically goes up.

 

[flyingscott]

First thing is get a tach, I highly doubt you are turning the rpms your tach says you are.

 

[Sea Rider]

At 5900-6000 wot rpm over revving hole shot should be superb, tach seems way wrong ?

Happy Boating

 

[SeaRay Seville]

Yep I figured the same after he told me my max RPM. No way it could be pulling 6000. It's the factory tach from 88. New one will be here Friday. So i found out the original aluminum prop is a 17P and the ballistic SS prop is also a 17P. Seems they should've put a SS 15P on correct?

 

[SeaRay Seville]

I mean it's not that bad, planes out in 4-5seconds best I could measure, I'm not sure what MPH I was moving when it planed.

 

[Sea Rider]

Try both 17 pitch with new tach and stay with the one that makes OB to rum at max 5250 rpm range as usually loaded, you already have 2, don't go for a third one if haven't tested both 17 with new tach..

Happy Boating

 

[SeaRay Seville]

Ok thanks, hoping to test this weekend but it's calling for snow tonight up here So excited for boating this year! Thanks everyone for the input!