Ryan Dykhouse

New Member
Jul 13, 2019
13
Boat Info
2004 Sundancer 300
Engines
(2) Merc 5.0’s
Set up is 2004 Sundancer 300. Twin 5.0 MPI's, Bravo III outdrives and 22 degree dual props.

Boat seems to have a cavitation issue. The boat is under powered in my opinion with the 5.0's and certainly with more than 4 adults, full fuel, etc. Has always had a difficult time getting on plane and I have to use the trim tabs to help it finally get over the hill.

However, 9 times out of ten it will either cavitate or something is slipping causing the rpm to go from approx. 3,400 to 4,200 for example. I'll then back off the throttle, furthing the issue of trying to get on plane. It will also have this issue at cruise in seas greater than 2'-3'. Issue happens on both sides but for some reason appears to be more prevalent starboard.

Thoughts or similar experiences?
 
in '05 they went to 20p props - never had a problem with my '05 - even loaded with 4 people, a RIB, genny and enough water and food for a week on the hook.
i never trimmed up the drives at all.....check your "celery sticks" and make sure the drives are all the way down - likewise, i never used tabs to get on plane.
if the boat had a fault, it was that it didnt like to stay on plane under 3400rpm or so - i explored drop fins on the tabs or hill marine 4x4 props but never pulled the trigger as it wasn't that big of a deal to me (only in heavy sea conditions)
 
I assume you mean "ventilation"? Cavitation is something completely different.

That boat actually runs nicely with the 5.0's and the B3's. First, always make sure your drives are trimmed all the way down every time you take off and smoothly advnace the throttle all the way. Then, don't trim up too high - based on the conditions. Also, use those tabs - they are a tool to help with getting on plane and running attitude on plane, along with adjusting to get a better ride. It is quite normal to use tabs - especially as the load in the boat increases. There's absolutely nothing wrong with having to use them - that's what they are there for.

Lastly... if there's ANY growth on the hull bottom, even just slime, it can greatly affect performance - along with prop or gearcase damage.

Otherwise, you're looking at engine power issues or a slipping coupler.

With just you onboard, it would be good to know what your max RPM is at WOT and trimmed up.

Edit: But, as mentioned above, that hull doesn't like a whole lot of up/out trim. But you'll know when you've reached the limit as speed will no longer increase and/or you get ventilation. This, of course, has to be done with a clean bottom.
 
I assume you mean "ventilation"? Cavitation is something completely different.

That boat actually runs nicely with the 5.0's and the B3's. First, always make sure your drives are trimmed all the way down every time you take off and smoothly advnace the throttle all the way. Then, don't trim up too high - based on the conditions. Also, use those tabs - they are a tool to help with getting on plane and running attitude on plane, along with adjusting to get a better ride. It is quite normal to use tabs - especially as the load in the boat increases. There's absolutely nothing wrong with having to use them - that's what they are there for.

Lastly... if there's ANY growth on the hull bottom, even just slime, it can greatly affect performance - along with prop or gearcase damage.

Otherwise, you're looking at engine power issues or a slipping coupler.

With just you onboard, it would be good to know what your max RPM is at WOT and trimmed up.

Edit: But, as mentioned above, that hull doesn't like a whole lot of up/out trim. But you'll know when you've reached the limit as speed will no longer increase and/or you get ventilation. This, of course, has to be done with a clean bottom.
Dennis I couldn't trim my '04 300DA at all. Zilch. Zero. Just the slightest trim ventilated. Kept it down against the hull at all times and used tabs to get on plane with heavy load.
 
I assume you mean "ventilation"? Cavitation is something completely different.

That boat actually runs nicely with the 5.0's and the B3's. First, always make sure your drives are trimmed all the way down every time you take off and smoothly advnace the throttle all the way. Then, don't trim up too high - based on the conditions. Also, use those tabs - they are a tool to help with getting on plane and running attitude on plane, along with adjusting to get a better ride. It is quite normal to use tabs - especially as the load in the boat increases. There's absolutely nothing wrong with having to use them - that's what they are there for.

Lastly... if there's ANY growth on the hull bottom, even just slime, it can greatly affect performance - along with prop or gearcase damage.

Otherwise, you're looking at engine power issues or a slipping coupler.

With just you onboard, it would be good to know what your max RPM is at WOT and trimmed up.

Edit: But, as mentioned above, that hull doesn't like a whole lot of up/out trim. But you'll know when you've reached the limit as speed will no longer increase and/or you get ventilation. This, of course, has to be done with a clean bottom.

It very likely could be ventilation. Pardon the
Dennis I couldn't trim my '04 300DA at all. Zilch. Zero. Just the slightest trim ventilated. Kept it down against the hull at all times and used tabs to get on plane with heavy load.

Same. Don't even think about trimming it up. Tabs only, and I do throttle up with them fully down.
 
Dennis I couldn't trim my '04 300DA at all. Zilch. Zero. Just the slightest trim ventilated. Kept it down against the hull at all times and used tabs to get on plane with heavy load.
I swear I remember using some when doing a WOT test - but definitely not much. There were a few hulls from that general timeframe that didn't like much, at all. Maybe it was the just conditions that allowed me to use a little? Or, maybe I'm just not remembering correctly! :)
 
Sorry to resurrect and old thread but recently joined the Forums. I have a 280DA with the same set up. Same ventilation concerns when trimming and difficulty staying on plane below 3200 (25-28mph) but less pronounced and mostly when heavily loaded (6+ passengers) . My original props were 3x3 and I went to the Mercrury XR 4x3 which were not cheap but it was night and day. All but eliminated bow lift and planes very quickly. I can now stay on plane at 2500-2700 at 18-20mph with no sacrifice up top (45mph). What a difference on a less than smooth day and my wallet at the pumps saving about 4gph at cruise :)
 
In my 98 290 with twin 5.0 efi. I leave the drives tucked in at all times. Only time i ever use trim tilt is if im in the shallows with freinds. Otherwords. Drives tucked in, trim tabs full down and power up. Use only tabs to make movement on boat. Not drives
 
In my 98 290 with twin 5.0 efi. I leave the drives tucked in at all times. Only time i ever use trim tilt is if im in the shallows with freinds. Otherwords. Drives tucked in, trim tabs full down and power up. Use only tabs to make movement on boat. Not drives
100 agree with your philosophy, trimming up gains me 3-5mph but is not a speed boat so rarely get past 40 unless it’s glass just to check WOT.
 

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