One year later and things do not seem right

[dogdoc]

It has been 1 yr since repowered with 2 df250 Suzuki on my 280 Marlin. Engines run fine, no problems there. Initial props from dealer were 3x16x21. Max rpm was 5200 wot, 40-42 mph. Went to 3x16x18.5 the Suzuki rec for my boat and now get 5880-5900 rpm and 40 mph. Cruise at 4100-4200 rpm 29 mph and 18-5-19.5 gph fuel burn.
What has always bothered me is how low the engines sit in the water. I originally thought that maybe it was the extra weight from the OX Yamahas. I am not sure of that now. The engines never tilted high enough to get the props fully out of the water. Trimming while running on plane does not seem to make the difference I would expect. Pictures show the level of the cavitation plate tucked in and trimmed up to parallel. My understanding is that it should be even with the bottom of the transom. They look low by inches. Engines are in the top holes on the transom bracket.
My thoughts are leaning towards raising them. Really looking for some advice.
Thanks

 

[seasick]

I just looked at some specs and Suziki says the motor should be mounted 2nd hole up on a three hole template.
It seems that the 16 inch diam is correct for the 250. Your two different pitches result in pretty decent slip percentages but 5200 WOT with the 21 seems too low. The 18.5 pitch looks better on paper. Perhaps the motor does need to be raised. up a notch. When comparing other folks experiences be careful to check that they have 250s, That motor has a pretty high gear reduction number. The 225 is different.

 

[SkunkBoat]

I have an old school transom and I have no experience with brackets or "integrated brackets" or "euro-transoms"
Some Marlin owners maybe have a better perspective

What I see... maybe I'm wrong...
Your motors are as low as they can possibly be
The running bottom of your hull angles up toward the transom, much like a bracket.
They look way to low.
When you raise them, and you probably should, you will have to start your prop search again.

What does it look like running? can you see the ventilation/cavitation plate? Is it buried?

 

[SkunkBoat]

As for tilting out of water.
Suzuki has a Tilt cutout adjustment ring on the tilt tube.
Also, the mounting of your steering cylinders over or under the tiller arm can effect how far you can tilt.

 

[Halfhitch]

I have always understood that a good rule of thumb for a starting set-up is, on a standard transom the anti-ventilation plate should be 1/2 to 3/4 inch above the keel/transom junction, when the anti-vent plate is parallel with the keel. For a stepped transom such as you show in your pictures, you raise the motor an additional 1 inch for every foot of set-back on any particular setup. That is what I use for a guide to start. Thats just me and what I have gathered over the years but there are professionals on this board that have mounted literally hundreds of motors so eventually you will probably be getting much more valuable and accurate info than I provide as they chime in.

 

[dogdoc]

This stepped transom thing is throwing me for a loop. Are you saying line the av plate even with the hull bottom before the step and then raise it one inch for every foot length of the step. Thus the av plate may or may not set level with the transom at the end of the step.

 

[Ekea]

ok, so first things first. your boat does not have the full length running surface. the bottom of the hull stops about 2 feet forward of the transom. you use the hull bottom as a reference point, NOT the bottom of the "euro bracket". the reason for this is that the euro bracket isnt in the water when on plane. that being said, for every 1 foot the leading edge of the engine is behind where the hull bottom stops, you want to be about 1 inch up.

it seems your boat is on a lift. can you get in a kayak/raft and put a straight edge on the bottom of the hull directly in front of a motor and see where that line falls relative to the anti-ventilation plate?

 

[dogdoc]

doing that today, follow up later

 

[dogdoc]

ok got under the boat. 52 in from transom step edge to front hub of prop. Pics show level of av plate intersection with transom at the step. The top of the angle alum. is approx 3.5 inches from bottom of transom. Av plate checked with a level and is level. Hub is 4.3 ft from transom, thus top of angle should be 4.3 in, thus leaving a approx 3/4 in to low. A little harder to measure but bottom of transom is about the level of the water intake, another spec I have read about. One hole up would put me at that point. Is it worth all the trouble. I would have to do the job during the 200 hr service and could borrow a bob cat to hoist the engines.
Thoughts??

 

[SkunkBoat]

Next ride, get on plane at 30mph with engines trimmed out to even with the first bar up on the gauge. Maybe one bump up from that...

With someone driving and looking where they are going, go back and get a picture of the motors and the water flow. Maybe it will be obvious you need to raise, maybe not...

Here is were I run. Sometimes I go one notch up above the first bar. Thats where it sounds right. After that it will blow out in a turn or hop.
Of course, your hull is different but it gives you an idea. Also, your tabs may change things. I don't use tabs but I gather that bracket boats need them.

 

[Halfhitch]

"Av plate checked with a level "

View attachment 33955 View attachment 33957 View attachment 33958

This statement in your post is not relevant unless your keel is also level. Again, the anti-ventilation plate must be "parallel" with the keel. Hold the aluminum angle under the keel and hold it up tight while sliding it back past the anti-vent plate. Then trim the motor up or down until it is aligned (parallel) with the aluminum angle. The distance is measured from the transom to the leading edge of the lower unit, not the prop hub.

 

[Don Davis]

I had to move my DF250 up 2 holes on my 228 Seafarer from the initial install height to get much better performance but it was well worth it

 

[dogdoc]

So looking at my hull/transom it appears to be quite flat at the rear 1/3 at least. It is difficult to check with level as boat is on a lift with bow up for drainage. To the naked eye seems to be flat.

 

[dogdoc]

I had to move my DF250 up 2 holes on my 228 Seafarer from the initial install height to get much better performance but it was well worth it

Did you measure before move?

 

[SkunkBoat]

So looking at my hull/transom it appears to be quite flat at the rear 1/3 at least. It is difficult to check with level as boat is on a lift with bow up for drainage. To the naked eye seems to be flat.

if bow is up and it drains, it is not "flat". You have to match the keel angle for the measurement.

 

[dogdoc]

bow is up because bow cables are shorter and bunks are higher in front, boat is slightly tilted

 

[dogdoc]

more better going to the leading edge. that takes me down to about 3.5 in which is where I am at

 

[Don Davis]

Did you measure before move?

Yes I luckily have a friend with the same motor and Seafarer so I used the straight edge off his keel and measured to the anticavitation plate and then measured mine and adjusted to get the correct height.