Engine Height and staying on plane at low speed

[PastTheBarb]

I have a 1997 2100 DV CC with a 225 two stroke Optimax. Im having trouble staying on plane at low speeds. It seems to ride a bit bow high. To stay on plane we get beat to death at sea. Ive been going round and round and what to do about it.
The options are many.

Change the prop.
I have a 16x13 aluminum 3 bladed prop. The fella I bought the boat from had a stainless four blade that he claimed gave it more stern lift and liked to cruise at 3200 RPM. Anything under 4000 and it comes off plane for me.
He took the pretty prop and gave me the the old one :-(
The big question here is what prop to go to. I dont know what pitch the other prop was.

Lower engine.
Currently I have two holes open at the top. The AV plate is two inches above the bottom of the transom. I get out of the hole in a hurry but have to run too fast for most conditions off shore.
I run with the engine trimmed all the way down.

Add trim tabs or permatrim.
I dont know how the permatrim could help keep the bow down if its out of the water when planning.

I know this has been hashed and rehashed on here many times. But Im hoping since the permatrims have been in use longer there is more data.
What would you recommend?
Thanks in advance,
Howard

And yes. I once took a hook past the barb in the first knuckle of my index finger that had to be surgically removed

 

[Brent]

A good post on Permatrim for recently . Do a site search
Here is m2cw
Add Permatrim , inexpensive and easy

Adjust motor height . Site Search on Verado . There a good discussion from Verado club With a graphic

Once dialed in , Prop to max wot rpm so does not to lug the motor and with on the heavy side- full has, gear , crew, cooler ,
Piano

start prop shopping
Ken at Prop Gods

4 blade prop gives more muscle and lift

Add big tabs , another sites search

 

[SBH2OMan]

If you don't have trim tabs, that seems like an obvious thing to do first (I can't imagine having a "real" boat without trim tabs)

But first try changing your engine mounting position - I found this to have a bigger effect than a Permatrim on my 2330. Then I would try Permatrim and lastly prop.

Props are an expensive "trial and error" exercise that I have found to be frustrating on every boat I've owned. Probably because I don't have a guy with a van full of props that will let me try one after another until I get just the right fit (like buying shoes at Nordstrom). I have to pay full retail for them and then sell them at 60% of retail if they don't work out (which they usually don't)

 

[Antidote]

Or you could go to Prop Gods or a similar prop shop that will pick the correct prop the first time. They also have a prop exchange policy that lets you send them back for another if they aren't damaged.

 

[SBH2OMan]

Or you could go to Prop Gods or a similar prop shop that will pick the correct prop the first time. They also have a prop exchange policy that lets you send them back for another if they aren't damaged.

I’ve talked to Ken a few times over the years. The cost of shipping back and forth to Florida (I’m in CA unfortunately) gets expensive quick.

 

[PastTheBarb]

Ken at Prop Gods suggested 15 pitch Powertech OFS4. https://propgods.com/shop/ols/products/ofs3 $500
its a 15 1/4 diameter 4 blade, normally gives good sternlift.
should help hold you on plane at slower speeds.
they are back ordered, so it won't ship for 4-6 weeks after you order, but its a good prop.
if you get one and decide you want a different pitch or style, you can swap out for $35 plus shipping.

Im leaning towards lowering the engine first. Ill let you know how it works out. Thanks for all the input.

 

[SBH2OMan]

definitely start with lowering the engine and see what that does. That sets your "baseline" for any other modifications.

One thing I recommend is to put together a table and capture the following data points before you move the engine mount:

RPM
SOG
GPH or MPG (depending on your instruments)
Time to plane (seconds) from a dead stop.

Take multiple data points every 500 RPMs while someone else drives (or you shout them to your helper). This will allow you to plot a graph and to calculate prop slip and general performance characteristics. Then when you try different mounting holes you're not just relying on your "seat of the pants" measurement to see if its actually better. Same goes for prop testing

Prop slip is a very important measure of efficiency. You can calculate it like this: 1-(mph x 1056 x final drive ratio)/(rpm x pitch). this will give you the amount of "slip" past your prop at various speeds. The higher the slip, the worse your MPG will be for a given speed

 

[PastTheBarb]

I still haven't lowered the engine yet. Yesterday I went fishing. At close to WOT the cavitation plate is well out of the water. I run with the engine trimmed all the way down. The front of the plate is about 3 inches out of the water and the back is about an inch and a half. If I lower the engine two inches (two holes) maybe I can run tilted up a bit to level the cavitation plate and it be closer to the water.

 

[SBH2OMan]

Did you capture any data? If not, anything you do to change will only be measured by “hmm it seems to feel different” but your brain can trick you. Having real data is better.

Make a table with the following rows:
500
1000
1500
2000
2500
And so on up to redline.

Now make columns for:

SOG
MPG (or GPH)

Make runs up to WOT and quickly capture the SOG and MPG data every 500 rpms. Make a note of where the boat is actually planing.

You can also make additional runs just timing how long it takes to get in plane.

Capture as much data after as many runs as you have the time & patience for. You will not exactly reproduce the same numbers each time, but when plotted in a graph, patterns will emerge. The more runs, the more data. The more data, the better the statistical relevance of your conclusions.

Now you have a baseline.

Lower the engine.

Now do the same thing over again. Plot the results on a new graph

Compare the time to plane

Compare the planing speed and RPM

Compare the MPG or GPH at your cruising RPM.

You will see the difference made in the data.

Now compare the empirical data to the way you “feel” about it. (Ride quality, etc). Make notes.

This will give you a much much better basis for further experimentation.

Good luck!

 

[PastTheBarb]

I can do SOG at different RPM but I dont have instrumentation for fuel consumption.
I was thinking about doing this in a local lake where the conditions wont change much from day to day.
The ocean or the bay is different everyday. Getting on plane may take a couple of seconds longer in fresh water vs salt.

 

[HOTPURSUIT]

I would start with lowering the motor