Hull Shape, Speed and Trim Tabs

[WSUDERMAN]

Re: Hull Shape, Speed and Trim Tabs

Alpine,<br />Something more basic but important. Look at the angle of your motor. The attack angle of your prop is pointed up! This will force the bow of your boat down and with that hydrofoil on there it will force your bow way down.<br /> I do not know if you have power trim on this, but i can see 4 holes for fixed trim adjustment and yours is in the hole closest to the boat. if you move this out and align the attack angle with your hull or even a bit down this will cause the bow to lift up and get you on plane. I would do this prior to any kind of tabs. Most tabs will force the bow down, not up. <br /><br />Besides this will cost you nothing to try (except gas)...

 

[Philip Stone]

Re: Hull Shape, Speed and Trim Tabs

SoLittle,<br />I'll keep raising the motor in mind. It is at the lowest setting on the motor mount. However it was installed by a very experienced shop and in addition I think the angle of my pictures exaggerates the position. There is another issue with raising the motor and that is losing the prop out of the water in larger swell. As for the prop, I'm taking nautiJohn's advice on that one and waiting to see what the tabs do first.<br /><br />78FourWinns,<br />It is the bow riding too high that I am trying to rectify, I need the bow to come down. I did play with the motor angle a bit a while ago but the only way is out and that exacerbated the problem. There is power trim and the way the motor is angled on the trailer is no indication of how it might be trimmed on the water I drop the motor low as per the manufacturers recommendation when trailering.<br /><br />The installation of the M120 rig has gone well so far. I have the tabs mounted and will sort out the HPU setup and helm control later today. Luckily I managed to climb under the rear bench and use a circular saw to cut a section of plywood out of the floor to get access to the tab mounting bolts and get washers, nuts and sealant on them. Bonus is I wanted to get a second bilge pump back there too (the previous owner mounted a pump way too far forward to be optimum, having spent some time under the bench I now know why he did!).

 

[Tabman]

Re: Hull Shape, Speed and Trim Tabs

Thank you for the reply John, I appreciate your comments. I will still disagree that boats less than 20 feet are not good candidates for helm controlled Trim Tabs. That size boat is a large sector of our market place, and we (and other helm controlled Tab manufactures sell directly to boat builders who regularly install them on boats under 20 feet).<br /><br />We feel that the remotely controlled Tabs are a better choice in the 16 to 20 foot range since the loading of the boat will have such an impact on its performance both for and aft and particularly side to side. The remotely controlled Tabs will allow the operator to better tune the boats running attitude on the fly and adapt to changing conditions.<br /><br />As I mentioned down here in Florida Trim Tabs are on just about any Flats Boats,(small, fast, light weight skinny water boats used to fish in the flats) that is 15 feet or above. They are most often installed by the boat builder. We commonly see Tabs installed on center console boats in the 17 – 20 foot range. The Genmar Logic Roplene boats use our Tabs in that size range.<br /><br />So we will have to agree to disagree, but I do have to make the point that remotely controlled tabs are indeed commonly installed on boats in this size range and provide more control over a wider range of speed, weight distribution in the boat and sea conditions.<br /><br />Tom McGow<br />Bennett Marine

 

[Jdeagro]

Re: Hull Shape, Speed and Trim Tabs

Tom:<br /><br />If Arnold S. can stay married to a Kennedy Democrat I suppose we can agree to deagree. Great Country, isn't it!<br />Regards;<br />John

 

[Philip Stone]

Re: Hull Shape, Speed and Trim Tabs

Okay the M120 tabs are installed and the tide is high at 7:30 pm this evening to get her back in the water and get the sea trials started. One last query before I back down the ramp.<br /><br />-the Doel Fin hydro foil, should it stay or should it go?

 

[red10]

Re: Hull Shape, Speed and Trim Tabs

lose it, it will not work good with tabs

 

[Tabman]

Re: Hull Shape, Speed and Trim Tabs

What red10 said, we suggest that you take it off so that its drag will not slow you down.<br /><br />Tom<br />Bennett Marine

 

[Jdeagro]

Re: Hull Shape, Speed and Trim Tabs

The excess stern lift at cruising speeds will make the boat run bow down, which will slow the boat and cause bow steering, or if you can trim the motor up enough to lift the bow ( prop is now fighting the hydrofoil) then you will loose speed because the prop is running at the wrong angle.<br /><br />If it slows you down it cost you money, in lost fuel economy. They are cheap to buy and expensive to run.

 

[Philip Stone]

Re: Hull Shape, Speed and Trim Tabs

Okay so here's the report. I took my kids overnight to an adjacent island, West Redonda. Great spot, a waterfall drains out of a large lake perched immediately above the saltwater. Very picturesque.<br /><br />Had a variety of wind and sea states en route from 2ft chop to glass calm. No doubt about it the tabs picked the stern up way more than the hydro foil ever did (and yes I did remove it thanks).<br /><br />I figure our top speed was 17 knots from a timed point to point crossing which is certainly the fastest I've had her at. However the revs didn't come up that much higher, at best 5,100 which is an improvement of 200-300 RPM from my past best but still well shy of the manufacturers recommended 5,750-6,000. I'd guess the speed has improved by 2-4 knots.<br /><br />I liked the added control and stability of the tabs they have a definite effect in bringing the bow down but I would stop short of saying we reached a plane. The motor sounded happier with its trim out at top speed instead of being tucked close in as I had to keep it before installing the tabs.<br /><br />So two questions remain: <br /><br />1- where do I find that missing 1,000 RPM? Is that in the prop? and would changing the prop to get the revs up have the net effect of increasing hull speed? That relationship I'm not quite understanding yet.<br /><br />2- what about lifting the motor a bit higher on the transom - does that generally have the effect of increasing rpm and/or speed?<br /><br />As it is I'm happy with the improvements in trim and stability but would still like to realize the full power of the motor.

 

[Philip Stone]

Re: Hull Shape, Speed and Trim Tabs

Wow, gotta keep the thread alive or I'll slip off you experts' radar!<br /><br />Luckily I pulled my boat back out of the water this evening and had a good look at the motor position, which gives me a reason to pick up my thread.<br /><br />Looks though the cavitation plate is a good 1" to 1and a half" below the hull (as measured at the transom). From what I have read here I should likely be raising it as much as 2 and half inches to get it 1" inch above the hull. Does that sound right to you guys?

 

[JasonJ]

Re: Hull Shape, Speed and Trim Tabs

I'd put it an inch above and try it out. You'll want to keep an eye on water pressure, if there is a steady stream from tell-tale at all speeds and in turns, its not too high. You may also end up with ventilation at the prop in tight turns with the motor higher. Don't know that you'll get 1000 rpms, but you never know until you try. I still think you may end up having to reprop. I'm no prop expert, but I would almost guess that a diameter increase and a pitch decrease would get it done.

 

[Philip Stone]

Re: Hull Shape, Speed and Trim Tabs

Thanks JasonJ, I just got back from local auto mechanic's. Used his engine hoist and lifted my motor to the highest point it will go (without redrilling holes on transom bracket) again luck was on my side and that puts the cavitation plate exactly an 1 inch above the hull. One of the mechanics there who seemed to know boats nodded approval as I measured the new height with my straight edge so I'm taking that as a good omen.<br /><br />It's not really a 'tight turn' kind of boat so I doubt that'll be a problem. As far as general decavitation goes I bet I'm fine, I've been raising the tilt approaching beaches and have been amazed at how far I can tilt up and still keep water intake in the water.<br /><br />I'll head to town in the next couple of days with my prop and get its pitch checked and purchase a differently pitched prop (I need a spare anyway so this one's a no-brainer). Weather is lousy so it won't be before w/e that I get her on the water again but I'll certainly report back after trying these modifications. Think I'll leave original prop on to test effect of motor raising then back the stern onto the beach and switch props and test that effect.

 

[BillP]

Re: Hull Shape, Speed and Trim Tabs

Originally posted by Tabman:<br /> Thank you for the reply John, I appreciate your comments. I will still disagree that boats less than 20 feet are not good candidates for helm controlled Trim Tabs. That size boat is a large sector of our market place, and we (and other helm controlled Tab manufactures sell directly to boat builders who regularly install them on boats under 20 feet).<br /><br />We feel that the remotely controlled Tabs are a better choice in the 16 to 20 foot range since the loading of the boat will have such an impact on its performance both for and aft and particularly side to side. The remotely controlled Tabs will allow the operator to better tune the boats running attitude on the fly and adapt to changing conditions.<br /><br />As I mentioned down here in Florida Trim Tabs are on just about any Flats Boats,(small, fast, light weight skinny water boats used to fish in the flats) that is 15 feet or above. They are most often installed by the boat builder. We commonly see Tabs installed on center console boats in the 17 – 20 foot range. The Genmar Logic Roplene boats use our Tabs in that size range.<br /><br />So we will have to agree to disagree, but I do have to make the point that remotely controlled tabs are indeed commonly installed on boats in this size range and provide more control over a wider range of speed, weight distribution in the boat and sea conditions.<br /><br />Tom McGow<br />Bennett Marine

I'm late responding to this but have to back up Tabmans comments... <br /><br />The suggestion of helm controlled tabs being dangerous due to rapid deployment is a big stretch of the imagination. No offense intended to anyone but I have kept my mouth shut long enough regarding statements about that. Your chances of this happening are the same as getting plucked off this earth by aliens. Helm controlled tabs are not that reactive...anyone who believes they are dangerous should take a test ride and experience it in real life. If a person has safety problems operating tabs they have NO business operating a boat either. <br /><br />If anyone wants to debate the "danger" of tabs...I suggest not being able to control the tabs are more dangerous because the boat cannot be adjusted to the changing conditions as noted by Tabman. The danger is more prominent in small craft at high speeds...60 mph bass and flats boats. With helm controlled tabs the speed can be stepped up and tabs deployed in unison to keep the boat from having unsafe quirks. No other tab offers that margin of safety.<br /><br />Bill

 

[rnsi]

Re: Hull Shape, Speed and Trim Tabs

Bill-<br /><br />While your comments make perfect sense, a big thing for me is I want to turn the key and go. The less I have to think about driving the boat the happier I am. Which is why I'll probably never own a sailboat.<br /><br />While the Smart Tabs may not offer me the precise control that helm controlled tabs offer, the offer me MUCH better control of my boat than no tabs, or a foil. The were much easier to install than helm controlled tabs would be - no motors, switches, wires. I predict them to be less troublesome - less stuff to break down. The only thing to break is the actuator, which is easily replaced. And they cost half as much as the helm controlled tabs.<br /><br />Most importantly, aside from the gains in preformance and handleing, is the fact that I don't have to think about them, and I can let someone else drive if I want to.<br /><br />But that's just me.

 

[Philip Stone]

Re: Hull Shape, Speed and Trim Tabs

In my brief but attuned experience with the helm controlled tabs I'd have to agreee with BillP. The response of the tabs is not so fast as to throw my boat around at all. I could see a single tab down causing erratic sterring but otherwise I'd agree that the gains in stability outweigh the slim chance of misuse. The rocker switches are stiff enough that accidental deployment is also very unlikely.<br /><br />And as for rnsi's remarks, I think that is totally valid and for me it was exactly the opposite case I wanted to learn more and have more to deal with. Helm controlled tabs seemed an obvious addition to my boat once identified as a solution to my boat's attitude behaviour and met my interest in learning more about running a boat.

 

[Jdeagro]

Re: Hull Shape, Speed and Trim Tabs

BillP;<br /><br />The issue of rapid deployment never came up. Bennett has always made slow reacting Tab systems for the very reason that if they reacted faster there would be a potential handling problem, and the company is very mindfull of safety and reliability. They build a good product and excellent customer service.<br /><br />Even with slow changes you need to keep in mind that the larger the plate, the faster the boat , and the lighter the boat weight, the more effect the tabs will have with even a slight change.<br /><br />There is no question that someone who is comfortable with helm controlled tabs can opporate them safely. <br /><br />My contention is that there are many people who do not take the time to learn boat handling, have many other things going on in addition to simply driving the boat (towing water toys), and/or allow other people who may not be familiar with the boat to act as the pilot, who can get into difficult situations. Good and sound safe boating practices eliminate most of the the potential hazzards, but too many people do not opperate boats with this caution.<br /><br />With regard to not being able to control Smart Tabs from the helm, what you need to understand is that the plates are never rigid, and therefore can only exert the amoount of force that the actuator load permits. They never act like fixed planing devices such as "Step and Trim" or Hydrofoils.

 

[BillP]

Re: Hull Shape, Speed and Trim Tabs

Ok, I'll clarify my earlier post and it is about mis-information, NOT product bashing....<br /><br />In my humble opinion, ANY and ALL suggestions that helm controlled tabs are dangerous (or more dangerous than "other" tabs promoted here) is a GIANT stretch of the imagination from the twilight zone. <br /><br />Also, the suggestion that helm controlled tabs are confusing or difficult to learn or use is also VERY unreal. If you have trouble zipping your pants up or brushing your teeth then MAYBE you would have problems controlling tabs. Like I posted earlier, if you have problems with helm control tabs you shouldn't be at the wheel of a motorboat. Don't make a decision NOT to buy helm controlled tabs based only on them being too difficult to operate...it isn't a problem for 99.99% of the population.<br /><br />It doesn't matter how smarttabs work compared to fixed or helm controlled tabs. Statements made about danger or difficulty on helm tabs are highly inaccurate. Many of the users posting here are first time tab users and don't know the difference. Tabman's forum on another web site (not Bennett's) has 100s of experienced users that can clarify real issues VS bogus ones.

 

[Philip Stone]

Re: Hull Shape, Speed and Trim Tabs

Well I hope to ease CrazyCharlie's mind a little because I'm just back after a full day on the water testing out my new motor, prop and tab setup. In very large part arrived at from advice and information I picked up from this and related online forums.<br /><br />So here's my recap of modifications and results as best I've measured or observed them.<br /><br />1- Tabs installed as mentioned in past message, working great, bringing bow down and trimming laterally as passengers move about works perfectly. Planes well and attitude allows me to trim up motor at top speed. If space on the stern had allowed I probably would have installed bigger tabs but there isn't much room so I put the largest I could fit. Overall stability is noticeably better. WOT rpm rose from 4,750 to 5,100. Speed (measured) up from 15 knots to 17 knots.<br /><br />2- Raised motor 2 and half inches and switched prop from 13" pitch 3 blade to 11" pitch 4 blade. WOT rpm now at 5,500 and speed estimated at 18-20 knots. Motor runs quieter, faster and prop feels like it holds the water more firmly. Wheel feels steady yet responsive. <br /><br />So I'm really pleased with the results. I think a little extra weight up front wouldn't hurt but I plan to install one or even two new batteries (to power the new bilge pumps I installed) in space in the bow so that will help. There's still 500 rpm I could pursue I guess, the prop shop has a 9" Yamaha 4 blade prop they say should fit but I think I'm content with where I'm at.<br /><br />Thanks all you guys for the great advice in this thread and others I have read. I've been joking with my buddies that I learned more in a week reading online than I think the staff at the dealership I bought my motor from know. All due respect to them but I guess you just don't log sea time working in a store. So thanks and any of you should check out the waters in our area if you plan a trip. Check out this site (it's one I designed) <br /><br /> http://www.discoveryislands.ca

 

[JasonJ]

Re: Hull Shape, Speed and Trim Tabs

Glad its working out for ya. Happy boating...

 

[Philip Stone]

Re: Hull Shape, Speed and Trim Tabs

Another day on the water, a different load and some even better results! Perhaps a little more experience too! Anyway I got the WOT rpm up to 5,750+ and I measured speed on a timed point to point run (on mirror glass water) at 21 knots. So there you go, optimized!<br /><br /> Thanks again you guys for the advice and I'll drop the thread now. Cheers!