Larger Trim Tabs or 4 Blade Props on a 320DA to get the bow down.

Discussion in 'General Discussion' started by MorichesBayBum, Apr 19, 2013.

  1. MorichesBayBum

    MorichesBayBum New Member

    24
    Jun 25, 2010
    East Moriches
    320 Sea Ray Sundancer
    5.7 Horizons/v drives.
    I am thinking about putting larger tabs on my 2003 320 DA. I have to run it pretty hard to get the bow down. I have V-drives and I have to run at 3800-4000rpm to get the bow down.
     
  2. hottoddie

    hottoddie Well-Known Member

    Jan 11, 2012
    Boston/Cape Cod
    1986 Sea Ray 390 Express
    Garmin 4212 Chartplotter
    Garmin 24 HD Radar
    Garmin GSD 22 Sounder
    Garm
    454 Crusaders
    This a such a common problem on many production boats, especially if they have V Drives. I have redone my own 390 and am helping a friend enlarge the tabs on his 1986 340 Express. I know several owners of 320-330 and 340 Sundancers that have either widened and/or lengthened their tabs with amazing results. My own 390 now stays on plane @2900 rpm @ 17-18 mph and 19-20 mph @ 3100 rpm with the 4 barrels closed. Bennett does not like to see the tabs lengthened but it is done on regular basis by many boaters. Usually done as a DIY project as many dealers/mechanics don't want the liability. Ironic because keeping the bow down improves visibility ride comfort and fuel economy.
     
  3. MorichesBayBum

    MorichesBayBum New Member

    24
    Jun 25, 2010
    East Moriches
    320 Sea Ray Sundancer
    5.7 Horizons/v drives.
    Thanks for the replies. The boat is miserable to run under 3800rpm @ 24mph. If I run slower I am squatting and throwing a huge wake with the tabs buried. If I run up in the higher rpm and speeds I can pull the tabs up and the bow will stay down.. As soon as I pull the throttles back to run a 3600, I slowly begin to squat. I pack light and any of my heavy item are up in the bow. I have a ton of storage in the stern and I don't use any of it. I also want to buy an inflatable but I haven't because of this issue. What are a good choice for 4 blade props?
     
  4. northern

    northern Well-Known Member

    Jan 17, 2007
    West coast Vancouver to Alaska
    380 Aft Cabin 1989 GPS and Charts by Nobeltec
    Twin 454 strait shaft
    hottoddie
    Did you have to change the cylender on the tabs or modify the pump system?
    Sounds like a quick fix for my problems. Boat will only go 18 knots with all the extra weight we put on it. Originally we could do 22 knots.
     
  5. Alex F

    Alex F Well-Known Member

    Nov 14, 2006
    East Coast
    2005 420DB with AB 11 DLX Tender, Raymarine Dual E120 MFD/Radar/XMWeather, ST7001 A/P, AIS, SeaLift
    T-Cummins 450Cs Straight-Drives, 9KW Onan Generator, 40HP Yamaha for tender.
    Based on what you described there are clearly various things to review here before investing in either new tabs or new props. I've owned 320DA with 5.7MPI V-drives for 4 years and it did pretty good with 3 blade props and standard tabs. She would stay on plane with no problems at 3200RPMs. I always had a dinghy on the swim platform (~140lbs with a motor). My normal cruising was at 3600-3650RPMs that would give me 24-26mph (depending on seas, wind and current, of course). If I recall correctly, I would need about 1/2 tabs at the most.

    From you posts I'd say that my flags would be:
    1. "3800rpm @ 24mph" - this is too slow at these RPMs. She should give you 24mph at 3600rpms
    2. "As soon as I pull the throttles back to run a 3600, I slowly begin to squat" - this is to be expected from 4000rpm (for example) but she should ride fine at 3600rpms with 1/2 tabs deployed.

    At this point the most important question is what's your WOT RPMS and Speed?

    How long have you owned the boat? I'm just trying to understand if it's a new to you boat and you used to cruising faster on other smaller cruisers, then you just have to get used to the running angle of 320s. She's known to run slightly bow high. It's not a problem, it's just the nature of the beast.
     
    Last edited: Apr 19, 2013
  6. MorichesBayBum

    MorichesBayBum New Member

    24
    Jun 25, 2010
    East Moriches
    320 Sea Ray Sundancer
    5.7 Horizons/v drives.
    Again, thanks for the replies. The boat has 500 hrs, 250 hrs are from me. I have owned the boat for 4 years. I had the hull surveyed when I bought it. 2 years ago I had the bottom media blasted and barrier coated and repainted (It didn't need it, but I'm a finatic) I had the props balanced and checked out (they are to spec according to Bosler and Sweezy in Belport, N.Y.) I run WOT 5000 rpm at 34-35 mph with low fuel, no canvas. No vibrations at all. The engines run perfect. I have the Rinda Scan tool to troubleshoot and diagnose it myself. The boat feels great at 24-26mph, but I hate running at 3800+ to get it there. I would be ok with cruising slower if i can get the bow to come down. I'm open to any and all suggestions. I figure many people have successfully addressed this issue. I have another 3 years with the boat before I upgrade to a 380 (as soon as my kids are out of daycare, $2000 a month will be freed up :grin:). I would like to get it right the first time to avoid trial and error. Thanks again!
     
    Last edited: Apr 19, 2013
  7. Alex F

    Alex F Well-Known Member

    Nov 14, 2006
    East Coast
    2005 420DB with AB 11 DLX Tender, Raymarine Dual E120 MFD/Radar/XMWeather, ST7001 A/P, AIS, SeaLift
    T-Cummins 450Cs Straight-Drives, 9KW Onan Generator, 40HP Yamaha for tender.
    Now we have a good picture....:grin:

    It sounds like she's running to the specs (I assume that your numbers were either recorded late fall before winterizing her or just now when splashed). May I ask, if you had her for 4 years why all of a sudden you need to change something to get the bow down, did something change just now?

    Anyway, here's my take on what you're trying to address:
    1. Extra weight at the bow - IMO, this is the best approach. There are few ways of doing this. You can replace the anchor line with all chain (get 250-300'). In addition, you can place more weight under the master berth.

    2. 4 blade props - people have good reviews on them for improved hole shut, better handling at low speed while docking, but not in regards to keeping the bow down. At least I haven't heard anything.

    3. Larger trim tabs - Yes, they will help, but no matter how you'll twist it and turn it you'll be creating more drag in exchange for lowering the bow. This of course will affect performance. IMO, extra weight at the bow will give better results (performance wise) vs. having the same affect from more drag with larger tabs or using existing tabs fully deployed.
     
  8. JVM225

    JVM225 Well-Known Member

    Apr 8, 2008
    Farmingdale, NY
    2002 410 Sundancer, Monaco Edition.
    3126 Cats.
    I would seriously look at a prop change. Bosler and Sweezy should be able to make some recommendations.
     
  9. hottoddie

    hottoddie Well-Known Member

    Jan 11, 2012
    Boston/Cape Cod
    1986 Sea Ray 390 Express
    Garmin 4212 Chartplotter
    Garmin 24 HD Radar
    Garmin GSD 22 Sounder
    Garm
    454 Crusaders

    Wow 18 knots. Is that @ wot? That's a stern heavy boat with the aft cabin even with straight shafts. One of the penalties you have with large prop pockets is the loss of lift in that area of the hull and increasing trim tab area is one way of compensating for the lost lift. My 390 will do almost 30 mph @ 4400 rpm and medium load. I removed the original SeaRay tapered tabs and replaced them with 30 X 12 that I extended to 15" and did not modify the hydraulics at all. I also took the original tabs and cut them down to 15" X 12" and fix mounted them between the tunnels for added lift. SeaRays are not the only boat brand that has this issue. Most V Drive and some straight shaft drive (like my 390) have this issue. There is another 390 @ my Yacht Club that has 454 Mercruisers and it has the same problem but he has yet to modify his tabs. People that have been on both boats comment on what a huge difference in how they ride
     
  10. Jetgod

    Jetgod Member

    150
    Dec 14, 2012
    Victoria,BC
    310 Sundancer 2000
    5.7 Mag MPI V-drives
    Larger trim tabs are an easy and effective way to inexpensively improve your boats handling.In this forum there are lots of folks discussing it and they have me convinced that it will be my first mod to a 2000 310 sa that I own.Do some more thread searching and you will find your answer. I plan on doing 3-4 blade props also but only next winter.You know,,money and all that.
     
  11. HUMPH

    HUMPH Well-Known Member

    Nov 4, 2009
    SF BAY AREA
    2003 410DA,
    2004 C14 Caribe
    CAT 3126TA's 350HP/
    50HP Honda
    I was going to go with 4-blade props if I kept my 320 longer. I was also going to extend the trim tabs the next time she was out of the water. Even if you installed the kits that turn the sides down it would help. Maybe reach out to "tabman" here on CSR as he works for Bennett and can guide you. All chain anchor rode would be beneficial as well.
     
  12. Havana Shamrock

    Havana Shamrock Well-Known Member SILVER Sponsor

    Sep 9, 2008
    Long Island.
    2005 500DB
    QSM11's,
    Honda 30HP
    Sea Doo 90 HP H.O.
    My 320 ran just like Alex's. with a dink also. My buddy's 320 was slowing down last season so off came the three blades in hopes of 4 blades and bosler and Sweeney said no! You need 3 blades but with a little more surface area , the thing jumps out of the water and is as fast as can be burning around 27-28 Gph he loves them . Just don't rush to through 4 blades on her. That's all.
     
  13. dpmulvey

    dpmulvey New Member

    Dec 19, 2007
    Homeport: Charles City, VA
    1999/2007 330 Sundancer Hardtop.
    6.2 Merc Horixons
    1.5:1 Velvet Drives
  14. CJ Martin

    CJ Martin Member

    762
    Oct 4, 2006
    Great Mills, MD
    2002 320DA
    350MAG Horizons / V-drives
    A couple of years ago Tabman advised me to try replacing the existing tabs with dropfins, and that did make a difference. He also recommended adding 12x12 normal tabs to each side just above the prop tunnel. He was confident the existing pump would be able to drive the extra tabs, so all I would need to do was tee off the lines. My plan this spring was to add the extra tabs as we are now carrying a dinghy on the swim platform. The furlough threat has postponed that mod.

    Four blade props are a much more expensive option - good luck finding a used pair and new you are looking at nearly 2 boat dollars. The extra tabs would come in around half a boat dollar for parts.

    Also I disagree that adding more tab increases drag. In fact by getting the bow down you are creating less drag. This is easy to prove by simply watching your speed as you add tabs. If the theory more tab = more drag were true, speed should not increase as tab is added (throttle held constant) but it clearly does as you reach your hulls "sweet spot" of running angle.

    -CJ
     
    Last edited: Apr 20, 2013
  15. hottoddie

    hottoddie Well-Known Member

    Jan 11, 2012
    Boston/Cape Cod
    1986 Sea Ray 390 Express
    Garmin 4212 Chartplotter
    Garmin 24 HD Radar
    Garmin GSD 22 Sounder
    Garm
    454 Crusaders
    CJ You are correct re: trim tabs will help reduce drag by improving running angle. In fact tabs that are too small need to be deflected to a sharper angle and will cause more drag than a larger tab deflected to a lesser angle. Before I modified my 390 tabs I had to run with tabs fully deflected and run up to 3500 rpm to get the boat on plane and then had to maintain 3200 rpm to hold on plane @ 17 mph and you could tell the boat was not running in it's sweet spot and the 4 barrels were open burning 30-32 gph. Now with 50-60% tabs the boat holds itself in a sweet spot @ 3050 rpm at 19 mph burning 28 gph. The boat is equipped with Garmin flowmeters and Bennett led indicators so I know these numbers are accurate. If I were to make any further changes it would be to replace the 19 X 18 three blade props with 21 X 17 three blade props for more blade surface area. I ran the 4 blade experiment on my last boat and found the the 3 blades with a slightly larger diameter and less pitch was the best combination along with very large trim tabs. :smt101
     
  16. IanBat

    IanBat New Member

    Nov 19, 2011
    Sydney, Australia
    Pro Tournament 36' 1999
    Twin Cummins 5.9L 370hp B Series
    For a quick easy trial, you could try throwing as much weight as possible up the front, get 2-4 people inside the cabin to sit up the very front or lay down, and see what difference it makes


    Sent from my iPad using Tapatalk HD
     
  17. Siboatguy

    Siboatguy Active Member GOLD Sponsor

    232
    Mar 28, 2016
    Holmdel,NJ
    2005 Sea Ray 320 Sundancer
    Twins V-Drives
    2017 5.7 Mercruisers
    I know this is a old page... But I brought a set of 4 blade props for the boat to install this spring... And debating on just having the trip tabs made a little bigger... Would love to hear how everyone else made out with there trim tabs and 4 blades if anyone changed them...
     
  18. hottoddie

    hottoddie Well-Known Member

    Jan 11, 2012
    Boston/Cape Cod
    1986 Sea Ray 390 Express
    Garmin 4212 Chartplotter
    Garmin 24 HD Radar
    Garmin GSD 22 Sounder
    Garm
    454 Crusaders
    Just my opinion but the trim tabs will do more for getting the bow down than the props. You can buy new larger trims tab planes and/or put extensions and the angled adaptors from Bennett.
     
  19. Siboatguy

    Siboatguy Active Member GOLD Sponsor

    232
    Mar 28, 2016
    Holmdel,NJ
    2005 Sea Ray 320 Sundancer
    Twins V-Drives
    2017 5.7 Mercruisers
    Was thinking about buying bigger ones... Do you go wider or longer??
     
  20. hottoddie

    hottoddie Well-Known Member

    Jan 11, 2012
    Boston/Cape Cod
    1986 Sea Ray 390 Express
    Garmin 4212 Chartplotter
    Garmin 24 HD Radar
    Garmin GSD 22 Sounder
    Garm
    454 Crusaders
    Bennett claims that wider (port to starboard) is better than longer (bow to stern). Measure the width of the mounting area you have available keeping in mind that the actuator has to be kept centered. Some people remove the existing tabs and have them modified at a sheet metal shop. I suggest having the edges turned down 90* and that will prevent the water from "sliding" of the edges off the tab surface.
     

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