Won't Plane out!

[1974-43MY]

So... I purchased a 43MY last September and brought it up the ICW - what a blast. It ran great - all systems go. After arriving in Annapolis, MD where she resides today... I realized I had some heavy smoke from the port side! So, I made the decision to have the port side motor re-built. I also did a ton of internal work, new wood floors, new Salon, counter tops.. it was a busy winter.

Finally, it was time to sea trial, several weeks ago we went out on a sunny day. We get to the mouth of the bay and out we go... after a few minutes we're in the mouth of the bay and power up... she will only do 12k ???(on the way up the ICW we easily pushed her to 18k).. After a few additional mishaps (intake impeller roached, then the fuel cooler, then the water pump) - yes it's been eventful... I sea trial again - same result. Hire a diver who cleans the running gear, bottom... I then get 14k, but she still won't plane out... The diver indicated that one of my trip tabs appears slightly lower than the other (we intend to inspect further tomorrow evening)... but regardless she won't plane out... So I have a couple questions for this knowledgable group:

1. With twin Detroit 671s on a 43DC MY - what kind of Knots do others get (both cruising & fully powered up?)

2. I know this might seem like a stupid question, but could one trim tab (slightly lower) actually prevent a 35,000 vessel from plane?

3. Is it at all possible that by adding the additional granite counters and flooring that I added too much weight to the vessel? (I know that sounds nutz but my worse nightmare is that I am the idiot that caused this problem)

4. Does anyone have any other ideas?

The motors seem to be running great - 2600 rpms, the transmissions are not slipping.... but she just runs like she's pullin' and anchor!

[Pascal]

if your 43 is anything like the 53 of that vintage, they dont' exactly jump on plane and they will need full trim tabs to get there. first thing is to make sure that the running gear is really clean but you've done that.... second is check that the trim tabs work and are fully down.

Weight can be an issue, any idea of how much weight you added to the boat? how much fuel/water/waste did you have on board compared to when you brought her north? check weight distribution too, did you put a lot of weight aft? try emptying the holding and water tanks before the next sea trial and most importantly, check the trim tabs first.

[Jaxfishgyd]

When we bought ours in 2000, it topped out at 18kts, but it was also empty. Now with all the "stuff" we have onboard (full time liveaboards) I top out at 15kts.
And to get it on a plane, I throttle up to full power (2450rpm), it will go on plane, I then throttle back to what I want to run. I cannot just ease the throttles up and have it get on a plane, it too pushes for a LONG time before maybe getting on plane.
But I normally run her in the 8-9kt range as the hull speed is just under 9kts and she does get good mileage there...

[Bill Allen]

My 1973 dcmy (6-71's310 h.p.) does struggle to stay on plane. They're a tad under powered to really plane nicely. That said I'm pretty much what everone else has said. I can plug along at around 14 kts planning needs tabs and of course with full fuel tanks need quite a bit to force the nose down. I won't be seeing much of that blistering 14 kts anymore, not at around 2 gallons per miles. I slow it down do my hull speed and get around 2 miles per gallon. With her full keel she's a pleasure to run and in the event you touch bottom the keel will save you a bunch of money. When I do push her to max rpm she is on full plane and is a totally diferent critter, BUT the screaming coming from my wallet really hurts my ears. Bill

[eze2bme]

My 1979 43DC with 6-71N's @ 310hp turns 2450 rpm's at full throttle ... and from what I've read here that's the maximum that you should be turning ... 2600 rpm's sounds way too high to me ... anyone??? Genesis???

[C. Edmund]

I agree to check how much weight was added -- and where.

I agree the trim tabs working properly could be a very big factor also.

Might also ask, was any prop change or pitch work part of your winter projects? That 2600 rpms sound high, like the props are not properly pitched.

[Will]

Our '80 43' DCFB has 485 HP 6-71TIBs rated at 2600 RPM. However, I've never had her up to more than 2400 running @ 18 kts. Other RPM/Speeds are 1000 RPM/9 kts, 1200 RPM/1000 , 1400 RPM/12 kts, 1600 RPM/14 kts, 1800RPM/16 kts.
Will

[1974-43MY]

Thanks to everyone who responded - much appreciated. I added flooring to the helm area (which is aft), the master bedroom, Salon, kitchen area and v-birth. I'd have to say I think much of the weight is in the Salon and kitchen area - fuel is about 1/2 full (2 180 gallon tanks). I've always known weight would be a problem, but I am a bit shocked that could actually degrade the performance of this vessel by so much.

I will be looking at the trim tabs tomorrow with my diver... maybe the additional weight requires the use of the tabs (didn't need them last year, she just planned out)....

Again, thanks very much - I don't mind typical problems (is there such a thing?), but this one.......has me frustrated and a bit perplexed!!

[Pascal]

when a boat is underpowered, it doens't take much to prevent it from getting on plane... a couple of hundred pounds in the wrong location and not enough tabs can be all it takes. try moving some weight forward (tool box and spares) even a passenger or two.

[Finalee]

My 1971 43 DC with 435 hp 6v92's planes at 2000 rpm tabs down giving 17 knots. She will stay up at 1750 rpm full tabs at 14 knots. WOT at 2350 rpm produces 22-24 knots 25% tabs. Sweet spot is 1900 rpm around 16 knots 50% tabs.