Trim/porpoising/GPH on a 2010 Sundeck 220

[Jdr01930]

We started the season early this year and launched April 9, since we really NEEDED to get out on our shiny new boat. It's fricken cold but we're lovin' it. Our local boat yard is letting us keep the boat at their dock pre-season till our normal mooring field opens in early May (Thanks Brown's!).

A few questions have come up - not sure if this is normal. On my old boat, after I'd get up on a plane I'd trim the engine up and get more speed/efficiency. On our Sundeck, any thing other than "all the way down" leads to a rather bouncy ride (I guess that's "porpoising"?). Any speed - typically we're not going much faster than 30 MPH (engine break in period). Also, when trimming up a little (and getting bouncy) I'm not really seeing any more speed or better GPH.
Is this normal, if so no big deal - it's just set and forget then, all the way down, all the time. With trim down ride is great anyway. Maybe I just don't need to do all that tweaking anymore. Any tricks/tips I'm missing?

Also - the stock gauge has GPH. Would be nice to see MPG too. Any way to get that other than mental math? The system knows speed and GPH so MPG should be easy for it to tell me... simple cheap mod/gauge to get maybe??

Will try to post some pics our our shake down cruise a little later.

 

[pchansen]

My '05 220 SD does the same thing (I know, different boat). I have a set of Smart Tabs on order and I'm hoping this will help. Others that have Smart Tabs can chime in but I believe these will cure your ills. As for MPH, I would love to have that data too. I don't know of any mod that can add that functionality to your Smart Gauges. I have a Garmin chartplotter and it will accept a signal from their fuel flow sensor and give the desired MPH. I just don't know of any way of interfacing Mercury's FF sensor with the Garmin chartplotter. I may have to add the Garmin sensor. It kinda seems silly to have two FF sensors, but that's what we'll probably be stuck with.

 

[Hampton]

I'm a little surprised they porpoise. Do they have trim tabs at all right now? I've owned 2 stern drive boats, a Classic 190 with a 5.0 and Alpha drive, and a 250 Da with a 5.7 and BIII drive. With both of these, once on plane, I trimmed up and they would accelerate to a point, then they would begin to porpoise if I trimmed up too far. From there, I would bump it down just a bit and get my max efficiency. Maybe they're designed to come out of the hole and run fast without trimming? Maybe the bows are just really light.

 

[pchansen]

My '05 220 SD does the same thing (I know, different boat). I have a set of Smart Tabs on order and I'm hoping this will help. Others that have Smart Tabs can chime in but I believe these will cure your ills. As for MPH, I would love to have that data too. I don't know of any mod that can add that functionality to your Smart Gauges. I have a Garmin chartplotter and it will accept a signal from their fuel flow sensor and give the desired MPH. I just don't know of any way of interfacing Mercury's FF sensor with the Garmin chartplotter. I may have to add the Garmin sensor. It kinda seems silly to have two FF sensors, but that's what we'll probably be stuck with.

I should clarify. Most of the time people (adults) want to sit aft of the windscreen. This makes the boat stern heavy. I can get the boat up on plane easy enough but it seems to run best with the drive trimmed all the way down, which I believe is past vertical and not the most efficient mode of operation. If I start to trim up, just a little, the boat will start to porpoise with four adults aft. I believe tabs (of any kind) will allow the boat to resist porpoising and give me the ability to trim the outdrive to a more neutral position and thus eek out a bit more efficiency. Time will tell. My Smart Tabs arrive on Monday.

 

[Jdr01930]

No trim tabs on mine.
I'm not sure anything is really "wrong" actually. If I just leave it down, the boat pops up onto a plane quickly and very evenly - it stays level/flat the whole time, and rides very smoothly.
It hadn't occurred to me though that the drive might be past vertical, as I've only seen it out of the water in trailering position. Once the water warms up here I'll jump in with a mask and see what angle the outdrive is at when all the way down.

A few pics from yesterday, just for fun:

 

[surfinjoe]

My smart tabs pretty much eliminated any porpoising. The ride is very smooth and I typically run around 40 MPH.

BTW - Nice hat

 

[jacktm]

I think once you get the weight of your passengers distributed better in the boat, that will go away. I always trim mine up

 

[Jdr01930]

I think once you get the weight of your passengers distributed better in the boat, that will go away. I always trim mine up

That's what my kid thinks, and it makes sense.
Right now, while it's so cold, he and I are the only ones dedicated (OK, crazy) enough to go out, so I can't test that theory.