Properly trimming a boat

[tomandwendy]

Hi,

I have just bought a boat and I have been searching for a way to explain proper trimming of a boat and how to start it. I think I have it figured out, but was wanting some insight or a link to detailed explanation of how to trim the boat out. I know when you start out, engine will be in the down position and as your plane out you will start trimming out and I do get good speeds and ease of turning, but I still would like to read a detailed explanation of how it works and proper techniques and what to look and feel for.

Thanks for your help.

Also I have a Evinrude 88 SPL and I am using 50:1 ratio....just double checking that I am correct.

Thanks

Tom



Forgot to add, I am referring to motor trim only, not the trim tabs or smart tabs.......

 

[180shabah]

Re: Properly trimming a boat

You are correct starting with the engine in the full down position, this provides extra stern lift to get you on plane quicker. If you leave the engine in this position you will still be lifting the stern which forces the bow down, this is very inefficient and can actually be dangerous on some boats. So now that you have the boat up on plane you want to trim the engine up. Just go a little bit at a time until you get a feel for how fast you setup reacts. Keep bumbing it up until the bow starts bouncing up and down(called porpoising) then trim down just enough to stop it. This will be your best running angle for that RPM and load.

In rougher water you may want to trim down a little more so you don't get beat to death.

 

[scoutabout]

Re: Properly trimming a boat

To build on what 180 was saying - -with your motor trimmed down, you are actually lifting the stern which serves to push the bow down. As you trim up the angle of the properller changes (so the direction of thrust changes) and you begin to exert downward pressure on the stern, which in turn pushes the bow up.

I'd agree it's pretty much a feel thing that will change with boat loading, water and wind conditions, etc. You identified one benefit -- the steering gets lighter (unless you have hydraulics -- then you might not notice). Another is a by-product of the most efficient trim setting, and this is maximum speed at any given throttle setting.

Here's a diagram from Mercury. If you look at the angle of the propellers in these pics you can see how the direction the motor wants to push (added by me in red) changes quite considerably with just a few degrees of trim change.

If you have a hand held GPS, use it to eek out every last knot from your trim angle. You'll notice as you trim up your speed will hit a maximum then start to tail off as either your prop starts losing grip, or porpoising begins to slow you down, or both.

Also, just a note of caution -- your boat will tolerate being trimmed up more (or "out" as Merc calls it) on a straight course much more than while turning. Point is, you could be charging along at WOT, trimmed up to within an inch of breaking loose, then decide you need to turn quick and sharp. This will usually break your prop loose almost instantly resulting in a possible loss of control, or at least very different handling characteristics you might not be expecting (or wanting) during a sudden avoidance manoeuvre or such.

Have fun experimenting far from other boat traffic. Oh -- and welcome to iboats!

 

[marine4003]

Re: Properly trimming a boat

My 2 cents....You mentioned trim tabs, i assume you have them, if so,prior to accelerating from a dead stop ,lower your tabs,this will lower your bow = better fuel economy,when the bow has obtained a somewhat even plane then trim using the engine, if you dont have trim tabs follow all mentioned above,trim tabs working in conjunction w/ engine trim,can save you alot of fuel.

 

[fishmen111]

Re: Properly trimming a boat

Welcome Tom! In no time this will become automatic to you. If you have a trim gauge, you probably won't use it much. One thing to add to these guys excellent advice is don't baby it coming out of the hole, drop the hammer to get on plane as fast as possible and then back off to your desired speed. You cause more stress on the motor by trying to gently come on plane. Yes 50:1 on your 88 as long as you are out of the 20 hr. break-in period (new or rebuilt). Have fun and be safe.

 

[tomandwendy]

Re: Properly trimming a boat

Hey thanks for all the great replies.....making more logical sense now to me.....matter of fact I have a trim gauge....it just never works lol. So is there a certain feel to the bow being to far in the water?? (not trimming up) I know my steering was pretty easy....but how do you truly know it is trimmed? I have a speed guage, but I am not sure at the moment it is working correctly because I top out at 41 mph.......it sure feels like I am doing faster then that, like at a 50 or 51......

Once again thanks for the great replies and I am sure I will have more questions!

Thanks

Tom

 

[Geo2008]

Re: Properly trimming a boat

I was just trying to educate myself on the same thing and found this article to interesting.

http://www.clubmarine.com.au/internet/clubmarine.nsf/docs/MG19-2+Technical

 

[fishmen111]

Re: Properly trimming a boat

To me Tom, I am properly trimmed at the highest rpm for a constant throttle setting without porpoising. I just "bump" the trim switch and hear the rpms increase a little until she either feels loose or bouncy. Trim back in a little and good to go. You cannot always go by a neutral steering wheel because the motor trim tab may be a little out of adjustment and/or the weight in your boat is different. Play with it next time out. You will have it down by the time you come back in.

 

[QC]

Re: Properly trimming a boat

To me Tom, I am properly trimmed at the highest rpm for a constant throttle setting without porpoising. I just "bump" the trim switch and hear the rpms increase a little until she either feels loose or bouncy. Trim back in a little and good to go. You cannot always go by a neutral steering wheel because the motor trim tab may be a little out of adjustment and/or the weight in your boat is different. Play with it next time out. You will have it down by the time you come back in.

I agree with this with possible addition that you can get increased RPM without porpoise but also be losing bite, you can feel this with the bump technique. If one bump down causes the RPM to drop AND a slight feeling of acceleration, then you were too high. Also, I would get as much weight out of the bow as possible so that you can use as much trim as possible. Very rarely does additional trim at WOT slow you down unless you are losing bite. Yes, porpoising will be the limit. This you control with trim tabs . . .

 

[lakergirltx]

Re: Properly trimming a boat

I'm assuming that the majority of the replies/advice are referring to a V-hulled boat, so I hope my coming questions aren't too off-topic here. I have been searching the threads to find info on planing and trim for a pontoon. Earlier discussions seemed to debate as to whether a pontoon can even get on plane (there were competing pictures). Or perhaps it's just not as big a deal as with V-hulls?

Our home lake is fairly large with long stretches at WOT to get to where I need to go, so anything that can improve performance and fuel efficiency I definitely want to do. So any thoughts on proper trimming for a pontoon? Follow the same steps as outlined for a V-hull? Next weekend when we're on the lake I'm definitely going to experiment to see how the boat reacts.

Also I'm assuming that smart tabs are only for V-hulls.

Thanks in advance!

Lakergirl

 

[fishmen111]

Re: Properly trimming a boat

Lakergirl, it is my understanding that pontoon design and hp determine that. The custom planing pontoons out there are very different with a straked, almost v-hull design. Most pontoons I have seen do not appear to have the angles or surface area necessary to pull up on plane. I would imagine though that with enough horsepower you could plane anything. Not a very good answer, just thought I would give ya my $.02.

 

[tomandwendy]

Re: Properly trimming a boat

Thanks for the replies, it is making more sense to me now....just one more question....what does "WOT" stand for?

 

[tomandwendy]

Re: Properly trimming a boat

I also had another off the wall questions, but with my evinrude 88 SPL, does anyone know if it has a high idle switch to warm the engine?? (When I drop in the water, it take awhile to get going, but once it has had a petal to the metal,, the rest of the day is start in a second) I saw that in another post.......also is it hard to convert a throttle to a foot petal? I saw one in gander mtn, and wondered how hard that would be and if anyone has done that.

 

[scoutabout]

Re: Properly trimming a boat

WOT = Wide Open Throttle

As for fast idle, look for either a secondary lever that you can raise to increase rpm in neutral, or a button on the main throttle that will release the gear shifting linkage resulting in throttle only response when you push it forward. To reengage the gear linkage, pull the throttle back to the neutral position. You will feel or hear a click as it goes into position. Then, the next time you push it forward, the gears will engage. Often this button is down at the base of the throttle lever at the pivot point. Older Johnson experts will be able to clarify I'm sure. I've got only Merc and Yamaha experience.

 

[SNye45]

Re: Properly trimming a boat

WOT = Wide Open Throttle

 

[tomandwendy]

Re: Properly trimming a boat

DUH! on the WOT......and I will look for that switch tomorrow when it is day light out. I hope it has one......most do right?

Also not sure if I need to start a new topic on this, but I want to powerload my boat but I am a little leary of it at the moment, right now just using a tow rope to push out and pull up, but usally takes a time or two because of the angle of attack I can only use. so my question is....what is proper technique to powerload onto a trailer that has no pcv pipe as guides. The hull of the boat has grooves with wood strips going bow to stern with carpet on them (not sure on the technical term of them, and also what is the best practice with the "boards" sticking out of the water to load the boat.

 

[scoutabout]

Re: Properly trimming a boat

Ah, powerloading. Yes, it really is a topic unto itself and you will find rabid defenders in both camps. Most will tell you not to powerload becuase you are destroying the boat ramp by eroding the bottom with propwash, causing sink holes or weaking the concrete ramp foundations. Others will tell you as long as you just idle on it's probably ok. Myself I'd say don't powerload if you can at all help it.
Start a new topic over in trailering and spell out the problem you think requires you to load that way.

 

[180shabah]

Re: Properly trimming a boat

I also have a bunk trailer and have on occasion had to load by myself. I did exactly as you did, used a line from the bow to pull the boat over to the trailer. One thing that will make a huge difference is how much trailer you have in the water. More is not always better(a common error made by new boaters). I dunk the full length of the bunks then pull forward until only about 2/3(or slightly less) is still submerged. With a portion of the bunks out of the water, all you have to do is get the bow between them(even up to a 90* angle) then pull the line straight to the winch and the stern will swing around. Hook the winch and pull the boat tight to the bow chock.

My bunks are set perfect for the strakes on my hull (They "pull" the boat straight and centered)so unless someone "helps" me with an extra shove is almost impossible to "miss" the trailer.

FWIW - this is a much safer option than power loading then hanging over the bow to hook the strap, then climbing over the bow and down the trailer.