TOPIC: Motor trim

I have a question about where to trim the motor on our old boats with out power trim and tilt.
Do you adjust the trim for getting on plane / hole shot, cruise or best speed? When I trim for good manners/ least hull slap I lose 5 mph off the top end and lose some fuel economy, But when I trim for best speed and economy it takes longer to get on plane and the bow is so high That I can't see unless I am standing up until I get up to well above planning speed.
The motor is a Mercury 400 with 5 trim positions. The boat is a 15' runabout with flat stern and v bow. I normally use 2 and 3 depending on the load but max speed is no 4 with no.1 being the closest to the transom.
I had a friend tell me that position 2 was the best because the boat got on plane faster and you could see while sitting down but the boat is a real slug in this position.
Fastest speed is 31 mph gps at 5600 rpm in position 4, in 2 fastest speed is 24 mph at 5200 rpm. Position 3 gives 26 MPH at 5400 rpm. position 5 gives 31 mph at 5600 as well but cavitation in any kind of chop or turn.

Trimming for top speed also means most fuel efficiency, since going faster with the same setup means going farther while using X gallons of gas. If you can deal with the bowrise, leave the pin at 4. If you want the best at all speeds and loads, its time to invest in an aftermarket trim unit. www.cmcmarineproducts.com/products/Outboard-Tilt-and-Trim/CMC-Tilt-and-Trim/CMC-PT-35-Tilt-and-Trim-for-up-to-35-HP

Sometimes it helps to redistribute weight in the boat, like moving battery, portable tank, tooolbox, or cooler forward a bit. Helps bring the bow down. Sounds like #3 is going to be a good setting.

Another thing, sometimes raising the motor up a little on the transom can make a big difference. Depends on some other factors, like the position of the cavitation plate relative to the bottom of the transom.

With my Glasspar, I had the same issues you're having, when I was running a fixed trim Merc 650. Finally repowered with a PT/T motor and now all is good.

My first couple of 'Glassics were manual trim set-ups, just had to pick the "happy medium" or best for whatever you were doing the most of that day - cruising, pulling toys, etc.. #3 hole got the most use as it was tolerable in all situations.

Once you get a PT&T setup you won't want to deal with this issue ever again, really makes life easier on you and I believe it makes life easier on your motor as well!

So it looks like #3 it is.
Is it common to lose 5 mph between trim settings? It just seems like an awful lot to lose.

I think mine was only a 2 or 3 mph difference, but it could vary by hull design, motor, etc. I guess.

Maybe try a piece of tubing over your tilt pin to find a middle ground between pin holes?

When my 17' aristocraft was in the water, with a Gale 40 hp, I found that putting the gas tanks under the bow made a HUGE difference in behaviour. I had similar problems to yours (the boat only weighs around 500lbs without engine/gas tanks), but with 2 6 gallon tanks under there, I was able to trim for speed and the ride was much improved. Of course the extra couple of feet may have exagerated the effects for me, but even 1 tank made a noticeable difference. I was able to move the setting from closest to the transom, to one or two out, depending on load, which increased speed and fuel economy - which kind of amazed me at the time as I was carrying so much more weight. Drag is a killer!!

The frugal knucklehead that had my Chrysler boat speced it without power trim on the 100hp motor. OK...But the kicker is, its a 17 footer with a back seat that is 4 feet forward of the transom and a HUGE motor well you could literally take a bath in. Chrysler used the same hull for the inboard and outboard in this model. Only changing the engine cover out for a splash well. To tilt the motor you have to climb over the back seat and climb into the motor well. Where the top of the motor is about knee level. If you could tilt the motor you would need the arm strength, and reach, of a orangutan. Seriously a safety issue. Pretty much means you set the tilt at the ramp and that's it. Or you and a close friend wade into the water to change it. For me there are few places where I go that there is a shallow spot to do that.

So you bet I have picked up a OEM T&T unit that is going on it in a week or two.

BTW To give an idea of the mind set of the PO. I found a FULL SIZE extinguisher under the seat. It had the name of a church he 'got' if from marked on it. He was the 'pastor' of that church.