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  Primer on Trim Please?

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Author Topic:   Primer on Trim Please?
JDH posted 07-19-2001 01:29 PM ET (US)   Profile for JDH   Send Email to JDH  
Can anyone point me to some good links on trimming out a boat? I am new to powerboats, and last night out crabbing with a guy who spent 10 years dealer prepping BWs. WHen I thought the trim should go down, he put it up - I could hear the motor run smoother and the boat accelerate.

So - I am looking for goals, pointers & references to help guide me as I begin to develop a feel for my BW.

TIA

Jim

Bigshot posted 07-19-2001 02:05 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Easy! You have to "feel" the boat, just like sailing. It is like tweeking your head or main sail to get the boat just right. There are also teltales for a powerboat. Ok! for starters, start with trim all the way down. Do not look at the guage, listen to the engine. It will make a different sound when trimmed "under".

Get on plane and as you are accelerating to cruise start trimming up. Lets say you are at 4000 rpm's to make it easy. keep trimming until the engine starts to cavitate and then bring it down til it grabs the water again. ill be like a slipping clutch. This setting is probably to high for cruise speed(ok for WOT) but now you know the MAX.

Trim down until you feel the nose start to boat start to slow or steering get tight. Look at the guage between high and this point and now you know your "range". Trim in this range until ou get the right adjustment.
On my Montauk with the 90 Yamaha the guage is between 2.5 and 3 for a good trim height.

Telltale are usually as follows:
1)porpoising-do not want that unless you like nausea.
2) wake will throw a kind of roostertail when trim is tucked in(all the way down). As you trim up, the wake gets wider and flatter. As you trim real high, it will start a roostertail on each side or sometimes more on the starboard side of the engine right at the transom. If you get haulin ass and trimto the gils, it will throw a real roostertail right behind the prop.

3) If overtrimmed it can start to chine walk at high speeds, equivalent to oversteer in a car. Basically you want the wake flat, the bow up a bit and light steering.

God luck and enjoy that little switch. Do not be afraid to trim.

Whaletosh posted 07-19-2001 02:18 PM ET (US)     Profile for Whaletosh    
Jim,

A) get a tach if you don't have one.

B) get some sort of speedometer; GPS, Fishfinder, pitot; anything as long as consistant.

Start out with the motor all the way down. Once on plane trim up. Watch tach, speedo, and LISTEN to motor. Speed will increase, RPMs will probably do so as well. Keep trimming up until motor stats blowing out or porpoising sets in. Trim down a little bit. You are close to optimum trim. The goal is to max speed while minimizing RPMs.

Here is a practical example. you get the boat up on plane and are cruising at 25 MPH, which is what you want. Trim the motor up. the boat should speed up as will the motor. Now you can back off the trottle some to get back at 25 MPH. Using less throttle to get the same speed yields more effeciency.

What is actually happening is the boat is rotating around an axis line, with the bow rising. This causes the running surface of the boat to decrease, plus on a classic Whaler or variable deadrise hull the hull that comprises the running surface is flatter and more parrallel with the surface of the water. It takes less power to pusht the hull through the water. Plus the axis of rotation of the prop is brought more parrallel to the direction of the boat, more effeciently using the thrust.


This isn't the entire picture though.

The most effecient very often will give a rougher ride. So, under some circumstances you might want to push the bow down by trimming the motor down. This will bring the more v shaped portion of the hull down into the water, and will allow one to cut through the waves more so than skipping over the top of them.


One thing to keep in mind is the usable trim range on some boats is fairly small. So you may need to bump the trim switch in short bursts and allow the boat to adjust a second before bumping the switch again.

With practice you will be able to "read" your boat by sight and sound. trimming the boat isn't a tough knack to get if you pay attention. I have gotten to the point that I don't even need to use the tach, I just listen to the motor.

Sean

Whaletosh posted 07-19-2001 02:25 PM ET (US)     Profile for Whaletosh    
Couple more pointers:

Trim needs will very with load and speed.

I don't trim when at WOT. I trim at cruising speed then open the motor up if I desire. I find this easier.


Sean

JDH posted 07-19-2001 02:33 PM ET (US)     Profile for JDH  Send Email to JDH     
Thanks guys -

I do have a GPS - the MPH on the fishfinder seems useless - too much turbulance being mounted on the transom.

I do need to get a Tach - Any reccs for my Suzuki DT-75?

Bigshot - I don't have any kind of guage on the TnT - just a button/rocker switch. BTW - We did get a little bit of rooster coming right off the prop area last night.

I have noticed the steering can be really heavy - I assume that means the bow is trimmed down too far...

Thanks for the great advice.

Bigshot posted 07-19-2001 03:04 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Rooster coming off the side is no big deal. Trim till your heart's content. Any tach wil work as long as it is for an O/B. Trim Guages are stupid on O/b's but funtional on i/o's in my opinion. Tach is the most important item. I like the teleflex sportsman series in white for a decent tach. Shop around for price. I run Gaffrigs in my Baja and they are sweet but major $$. I believe suzuki and OMC use teleflex as OEM.
Whaletosh posted 07-19-2001 04:06 PM ET (US)     Profile for Whaletosh    
Jim,

If your steering is heavy throught the trim range you may need to adjust the tab on the motor. If it is heavier in one direction than another, then this is even more proof that the tab needs adjusting. If it is heavy even at idle, you have a bind in the steering system.

But, if is heavy at full down trim and lightens up as you trim up then yes it is due to the trim angle. But, don't adjust the tab just yet. Figure, out at what speed you are going to be using the boat at most of the time, usually about 3/4 WOT. then adjus the tab for nuetral steering at that point, with the boat ptoperly trimmed.

sean

jimh posted 07-19-2001 09:08 PM ET (US)     Profile for jimh  Send Email to jimh     
The analogy to sailing is a good one. On a sailboat the helm pressure sends all kinds of feedback about the boat's sail trim. It is the same on a powerboat, as the steering will get a rather light touch when the engines are trimmed up and the boat is really running nicely.

When I was strictly a sailor I used to think that all there was to do on a power boat was to steer, but now I have found that there are as many--if not more--adjustments to tweak on a power boat as on a sailboat.

--jimh

Peter posted 07-19-2001 09:19 PM ET (US)     Profile for Peter  Send Email to Peter     
It is funny, after all these years having boats with power trim and trim gauges, I find that I have never really use the trim gauge to determine proper trim. All my trimming is by engine sound and feel.

A funny story relating to trim. I went out fishing with a work buddy in his very small walk around cuddy last year (obviously wasn't a Whaler). It was a beautiful warm summer day in July, hardly a cloud in the sky. Before we started out, he put up all of his canvas because he said that as soon as we start going, we'll get wet from the waves crashing over the bow. I couldn't believe this so I told him not to put the canvas up. He obliged and sure enough five minutes into the trip we were both wearing a wave. Prior to getting drenched I wasn't paying much attention to the boat and motor other than to notice that it was riding a little bow heavy, but I thought that was simply caused by the design (I'm not a fan of his boat, its way too small for a walkaround cuddy). Also, I couldn't really tell whether the motor was sounding good because it was a V4 looper, never heard one run at speed before, and I had been running a V6 cross charged on my 18 Outrage (the two engine types sound very different at speed). Well after a few more minutes into the trip, my work buddy asked if I wanted to drive (something I've never refused, when offered). As soon as I took the helm and put it up on a plane, I looked back at the motor seriously for the first time (I don't trust the trim gauges) and noticed that the motor was pretty much trimmed ALL the way in and seeing that I now thought that the motor sounded like it was laboring a bit. Before I started to trim it out, which was my first instinct, and thinking that this is not my boat so I don't know its idiosyncracies, I asked my work buddy whether there was some reason why it was trimmed all the way in. He looked at me with a very puzzled, but serious look and said "no". I then asked if he minded whether I trimmed the engine out. Still looking puzzled he replies "huh, a.... yeah sure go ahead" and I then started to adjust the trim and of course the ride characteristics of the boat immediately improved, no longer so wet being one of the primary benefits along with a much sweeter engine sound. Because of the remarks he made and astonished look he had concerning the improved ride, I then asked him if he had ever adjusted the trim of the motor and he replied "I didn't know you could do that."

Well to make a long story short, I then realized, laughing nearly hysterically, that he really had no idea that you could trim the motor with the switch on the thottle control and that he had been running around in this boat for three years like this thinking all the time that his boat had a really, really wet ride (I couldn't believe that as bad as I thought it was, it couldn't be that wet). He later told me that he thought that switch on the throttle was just for tilting the motor up and down. All this from a highly educated executive.

sport15er posted 07-19-2001 11:12 PM ET (US)     Profile for sport15er  Send Email to sport15er     
An incredible and hilarious story Peter, thnx for sharing the laugh!

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