Would changing pitch make a difference?

[emoney]

So, after all these years of owning boats, I'm finally publicly admitting I've never been very "prop educated". I mean, I've always had props. Shoot, I've probably even bought one or two over the years, but usually just got whatever some guy told me to get (hey, at least I'm honest). Funny too, as I've rebuilt outboards before, dropped plenty lower units always changing my own impellers & fluids. But I just don't follow the whole pitch thingy. So, that's why I'm here today. My name is Emoney and for 25+ years I've been prop ignorant.

Here's what I have: '95 Trophy 1802 WAC with a '95 Force 120. If you don't know the boat, they're a smidge on the heavy side. Currently, the thing has a 19 pitched prop. I'm very happy with WOT, hole shot and time to plane. What I need to know is would changing the pitch allow me to go SLOWER on plane? Yep, I just asked about going slower instead of faster, so what, I'm old, ok. Well, not really old, but momma loves sitting up front and she's a bigger fan of slow than she is fast. With the 19 pitch, I'm hitting the Service Manual's numbers pretty well I think as she will go over 5K rpms @ WOT and cruises rather nicely at about 3800-ish. Cruising speed currently is around 30mph, maybe a smidge below or above depending on water. Top end is 36mph-ish. What I'd like to accomplish is more like 25mph at cruising RPM. Can changing the prop, down I'm assuming in pitch, make that kind of difference?

Thanks in advance and sorry to be so "out in left field" when it comes to matters of such. Happy Labor Day, btw.

 

[Lyle29464]

Re: Would changing pitch make a difference?

You could go to a 17. That will slow down your cruise and help out all of your lower end boating. BUT remember the motor my be able to turn up Too many RPM'S now. So you need to watch it and not run wide open.

 

[jestor68]

Re: Would changing pitch make a difference?

Are you saying that your boat will not stay on plane at 25 mph?

Changing props is not the answer to attain a slower planing speed. Using a Doel Fin will allow your boat to plane off at a much slower speed.

 

[emoney]

Re: Would changing pitch make a difference?

My first thought was to add Trim Tabs, but not knowing much about how pitch affects a boat's performance, I figured I'd be better off at least asking about. You know what they say, "always go with your first instinct". Thanks all.

 

[Georgesalmon]

Re: Would changing pitch make a difference?

Planng speed is more a function of the boat hull shape than it is the prop. Yes you can reduce the planing speed by changing the shape of the hull. Many ways to do that including trim tabs, and those fins on the motor that I don't care for myself. Changing props can help a bit with say a four blade that lifts the stern higher. Changing the hull is really what you need to do. Anything you can leave at home? Weight is a big deal when planing too. Trim tabs will add surface area to the hull which will allow it to plane at slower speeds. The bigger they are the slower the boat will plane up to a point.

 

[emoney]

Re: Would changing pitch make a difference?

There's not a lot of excess weight on the boat. I don't carry a lot of gear outside of me & the missus, of course. I tend to keep quite a bit of fuel on board, and that's toward the stern, but really nothing else. The boat gets up on plane super fast, it's just that it wants to go off plane if you drop below the 25mph it seems. I keep the motor trimmed down, maybe I should start raising it a smidge? I really am considering trim tabs. I've ready both pros & cons when it comes to the "Smart Tabs", so not sure what to think there. I know that they're obviously quite a bit less expensive to purchase, but the biggest attraction for me is the "no operator involvement". I like to "dumb things down" as much as possible. I know there are automatic systems for the hydraulic tabs, but then the expense starts to really climb. Not sure it's a big enough issue to throw $7-800 at, if you know what I mean.

 

[Georgesalmon]

Re: Would changing pitch make a difference?

If you could move some weight forward it might help. Try running with less fuel, or if possible move some of the fuel forward just to see if your planing speed goes down. Trim tabs will help and since your only trying to solve one problem you don't need an eloborate system. I think you can get manually adjustable ones that have like a turnbuckle adjustment. They wouldn't work as well as smart tabs or hydraulic ones. Get the largest you have room to mount and adjust until you get the planing speed down. Will probably be so the aft end is just a little bit down from parallel with the hull.

 

[DC20]

Re: Would changing pitch make a difference?

I would go with Trim Tabs, slower planing speed, easier to get on plane and balance the load to sea conditions.
my 2 cents.

 

[HopinImFloatin]

Re: Would changing pitch make a difference?

i just added smart tabs to my boat, all i can say is they do everything they say. my minimun plane speed went from 25 to 20, takes off like a car-almost no bow rise, handles at low speed a bit better-not much though, reduced minimum plane rpm from about 3000 rpm to about 26/2700. i used to have a fin but took it off(came with the boat) and i really didnt notice much of a difference except a little less porpoising with the fin installed. No porpoising with the tabs. I was hesitant when i looked at these things being all plastic but it turns out that it was the best 120$ ive ever spent on this boat. and only took about a half hour to put on. 10 of it was deciding if i really wanted to drill holes in my transom. My boat is an 18 foot bowrider with a v6 and is very stern heavy. btw, they also reduced the amount that the stern drops when slowing. bought them here at iboats, easy peasy

 

[Lyle29464]

Re: Would changing pitch make a difference?

The fin and tabs advice is the best. I was reading something else into your problem.

Lyle