Speed vs motor placement, and load

TinBoats.net

Help Support TinBoats.net:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

TOY BOAT

Well-known member
Joined
Sep 10, 2011
Messages
183
Reaction score
0
Location
Dover, NH
Ok first off. I am a car guy. I understand cars and how to adjust/remove weight to gain speed. I am not looking to go faster, but to get the most out of my setup. I have been searching, and the answers I am finding seem to be different depending on who you ask.
So here is my questions. First off, where does the motor want to sit? I have read that the anti cav plate needs to be in line with the bottom of the hull. I have also read that many people have it just below by an inch or so. Also from a speed standpoint, do I want the plate parallel with the hull, or just slightly tipped down to force the bow down? Do I want the bow in the water, or out of the water for speed? I am guessing out of the water.
Now for weight. Do I want the weight mostly in the rear, or spread out towards the front? I was thinking the battery up front, the fuel tank in the middle, and me in the rear with the engine, but I have read people talking about keeping weight in the rear. Again, I am looking to get the most power out of my set up, as my wife and I do not fish, we just cruise around.
I am just looking for the best overall setup for cruising.

Thank you
 
I prefer more weight up front because I usually find myself out alone more than accompanied as less tilt is required to get on a plane, which is ideal for cruising. When riding by yourself, or with your better half I would adjust the tilt pin until you find which will work best w/ and w/o additional load. Past boats I would adjust the pin in when someone came along as it made a great difference since previously It was all the way out to keep the boat from porpoising, or bouncing while under load. The point before the bounce starts is the fastest it will go comfortably. Less weight will also make it a lot faster. Battery, cooler, etc.
 
There are no absolutes, and everything is a compromise. :) The best way to answer your question, is to do your own testing with your hull/motor/load combination.

In general:

Cav plate near parrellel to bottom, in range of 1" above or below. Higher is slightly faster, but make sure you have good water coolant flow, and don't cavitate prop on turns. Unless you are modding transom, you can only adjust about 3/4" shim (higher) with most engine clamp mounts.

Weight, balanced or slightly bow heavy helps get on plane quicker. Best speed is usually with weight back toward stearn. The more hull out of the water, the faster. Test by moving passengers and gear around.

Trim angle: Parrellel is usually best for small boats with fixed trim positions. Slightly out can help get bow out of water and more speed, but getting on plane will be harder. Easy to test, and not worth settling on an exact position, without.
 
Basically it all comes down to drag. Contact with the water creates drag. You want to minimize that in order to get the best speed and efficiency. Running the boat level may not be better because you are maximizing the surface area in contact with the water, however, you are raising the boat out of the water also so there is a trade off and it is based on speed to a point. The only way to know for sure what the best set up is to get out on the lake and run the boat with different set ups and see what gives you the most speed. Use a gps to record speed. I would think that if you are getting more speed you are probably getting better efficiency too, to a point.

The best way to mount the motor is to mount it as high as possible without it ventilating. I would start 1” over the bottom of the boat. If you can run it without it venting including turning then you are golden. If it vents, try dropping the motor using the tilt pin one notch at a time. Too much tilt under will cause heavy steering so don’t tilt it too far down or be ready for it.
 
I have been told by a couple of people that know more about boats than I do, to put the weight forward in the boat. One reason is that it gets the stern higher in the water, so you can get through shallower water.
 
Since it appears that all of your adjustments are static...not dynamic...the above suggestions are right on.

IF YOU HAD.....

Think of a boat/motor combo that has dynamic (adjustable ) options.

Hydraulic jack plate.... boater starts off with the motor down to get the most "bite"...raises the hyd/jack plate up as speed and planing begins. Boater ends with hyd. jack plate at top (engine at highest point) for maximum speed. Water flow to the motor is minimal, but sufficient to still cool the motor.

Hydraulic tilt and trim...boater starts out with motor "tucked in" i.e. engine shaft closest to the boat... speed increases...boater starts tilting the shaft further back...to get more speed...
.....Then..motor tilt is set at a greater angle....
....boat starts to porpoise,...boater tucks the shaft in ...just a touch..... for max speed.
Boat is riding on its "pad" positioned right at the stern.

Since you don't have all of those hyd. adjustments,...anything you do will be a compromise.

regards, R
 
Thank you for the replies =D> . While I do understand a lot of it, I guess getting the boat out and trying different combinations is the only way discover what works best for it.
 
That is the best way to get your setup right.

Just remember that changes in the weight; crew; waves; wind will all affect the final results. You may have to set her up one way with just you aboard...and another when you take someone out with you. R
 
I really needed to know what different settings would get me, and everyone answered that. Thank you.
Now that I have an idea what certain settings will do, I can adjust with some sort of direction. Before this thread, I no idea what a particular setting would do to boat performance. Like I said before, I am not really looking for more speed. I am however looking to be more efficient with what I got. More speed would be cool too. Here is a pic of my wife and myself flat out as we take off.
With these pics, the cav plate is 2" below the hull, full tank of gas, and battery both placed behind me. She was running 23mph here.

SSPX0232.jpg

SSPX0231.jpg


At idle.
SSPX0230.jpg
 
23mph with that boat, load, and 15hp is decent.

I'd try moving weight forward first. Have your wife sit in the bow seat. You will probably plane quicker. Speed wise, it might not change, but ride may be a little rougher/wetter, too, depending on chop.

You can raise motor 1/2" - 3/4" by putting a piece of plywood on top of transom. Make sure your clamps still have good bite. Higher than that will mean transom mod or mini-jacker.

Trim position: try one pin in from current setting and one out. In will force bow down, out bow up.
 
lckstckn2smknbrls said:
I would rise the motor 2" so it's level with the bottom of the hull.
I have already started to make a 2" jack plate. I will try that first, then I will try moving the battery to the bow seat, and the fuel tank to the mid seat. I figure the more mph it runs at WOT, the more efficient it will be.
 

Latest posts

Top