Will trim tabs expand operational cruising speeds

bobdec

Petty Officer 2nd Class
Joined
Aug 12, 2010
Messages
170
Had about seven different boats and about just as many hull designed in my boating background. But this is my first offshore type. It's a 1996 Pro-line walk-around cutty model 201 (Stalker) with a 150 Merc OB, 14 X 19P SS prop. Probably near 4000 lbs loaded w/fuel, people, gear, etc.
Here is my question.. this boat runs 2.5-3 MPH (GPS) at idle speed 550 RPM, can run in displacement mode up to 7 MPH at 1200 RPM. And then it starts plowing the stern and digging in over 1200. If you give it throttle it planes up very quickly at 27 MPH and 4000 RPM even w/4 passengers and full tank (70 gallons), top speed is 42 MPH at 5300 RPM so the prop pitch looks about right for the HP. My problem is it sort of limits my running speed selection, I either have to run under 7 MPH or above 27, I normally cruise at 30 MPH holding close to 4000 RPM. If if falls 200 below 4K or 27 MPH the boat starts to loose plane. Its a fishing rig 90 % of the time, but I have used it to pull the grand-kids on tubes, however the boat rides like heck trying to hold it at 20 MPH (kids are young) the stern plows down and it takes constant throttle adjustment to hold the speed steady as it oscillates trying to get itself on plane. Is this normal for this type of hull deadrise is 19* ? Would some Bennitt (M120's) expand my operational choices.
 

QC

Supreme Mariner
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Mar 22, 2005
Messages
22,783
Re: Will trim tabs expand operational cruising speeds

Properly sized tabs will probably reduce your on plane speed to be below 15 MPH. You can also reduce your idle speed for trolling. If installed and understood and operated properly they should not reduce top speed.

For anybody else that asks, "should I get tabs" (popular question last week or so). The answer from me is always "I believe they should be standard on all V-hulls and helm adjustable tabs will allow you to do things with your boat that you never thought possible. Those that say you don't need them either have not used them or do not understand how to use them."
 

Don S

Honorary Moderator Emeritus
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Aug 31, 2004
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62,321
Re: Will trim tabs expand operational cruising speeds

You aren't one of those guys that uses a trim gauge, and you set it where the needle points to the proper place and call it good are you. Have you tried trimming the motor down at lower speeds to help lift the stern out of the water to pick up rpm. Motor trim is something you have to do constantly for proper control. If the motor won't help lift the stern, then yes tabs will help. And I agree with QC. any one that has learned to use them (and it's not rocket science) you will never live without them.
 

steelespike

Supreme Mariner
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Apr 26, 2002
Messages
19,069
Re: Will trim tabs expand operational cruising speeds

Usually tabs will improve handling,ride and ability to stay on plane. But from my limited reading
of tabs tested as you apply the tabs it it can use slightly more fuel.The best mph and/or speed was with the tabs fully retracted.
Again very slightly. Another solution is a 4 blade prop in an 18".It should stay on plane better at reduced throttle, handle better
on plane and around the dock.It may reduce top end slightly.If the prop can improve your slip speed may remain close to the same.
If your gear ratio is 2.00 your slip is about 12% if 1.87 slip is closer to 17% 12% is toward the high end of normal
Is the 42 mph with your typical load?
While a ss four blade is pricey I think less than tabs and of course less complicated.
 

bobdec

Petty Officer 2nd Class
Joined
Aug 12, 2010
Messages
170
Re: Will trim tabs expand operational cruising speeds

I'll try to answer some of the questions.. I always adjust the trim for the the best RPM as soon as goes on plane after leaving the marina. This setup has the 150XL longshaft OB w/a deep transdom, drafts 33 inches with engine down. If I trim to far down the anti-cavitation plate starts throwing spray, if to high a rooster tail starts growing. Either one of those will drop he speed/RPM, so I find the sweet spot where she is happy, best ride, lowest RPM for holding 30 MPH with load. I very rairly run it at WOT 42 MPH, only when necessary under certain conditions, I would assume 42 is ideal and would drop if load and conditions deterate. The gearcase is a 2.00:1 on this engine. I was thinking about lower pitch prop, but my problem doesen't feel like a lack of power, just feels like the hull needs to go fast to hold plane and as soon as it looses speed it wants to come off. If I could keep plane even 10 MPH slower at 20-22 MPH as post#2 implies the $600.00 for a set of tabs is a no brainer for me. Now that I think of it the two cruisers I have had in the past a 26' 1966 Owens Sea Skiff (I repowered w/a 350 SBC) and then a 24 ' Bayliner Sun Bridge (305 SBC) both had tabs, I just thought the smaller 20' w/150 HP Pro-line would not need them.
 

QC

Supreme Mariner
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Mar 22, 2005
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22,783
Re: Will trim tabs expand operational cruising speeds

I have large extended tabs. My 23 footer with an I/O and 20 degree bottom can hold a plane at 12 MPH. I said 15 to be conservative :)
 

Mischief Managed

Lieutenant Commander
Joined
Dec 6, 2005
Messages
1,928
Re: Will trim tabs expand operational cruising speeds

Trim tabs will absolutely lower your planing speed. Get the biggest that reasonably will fit.

I use mine so much that I have two sets of switches for them, one set I can reach comfortably while sitting (these came with the boat), and one set (that I added) that are perfectly placed for operation while standing.
 

cyclops2

Banned
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Apr 19, 2011
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1,237
Re: Will trim tabs expand operational cruising speeds

Remember guys.
All OB & IO drives WANT to become a inboard with a prop shaft & PROP UNDER the hull.

Real inboards can and do rise straight up onto a full plane with ... NO... NO.. hole shot or climbout angles to speak of.

But "" I do not want a utility boat . "" "" No dog house in my boat. ""

O K :)
 

dingbat

Supreme Mariner
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Nov 20, 2001
Messages
15,417
Re: Will trim tabs expand operational cruising speeds

Falling off plane at higher speeds is the normal for that kind of a hull. Anything under 21-22 kts and I'm off the running pad. Anything under 20 kts and I'm on the way off plane. Tabs reduced my planing speed maybe a knot or two at best. I had better luck going to a high lift prop to keep the rear end from wanting to sink on me.

IMHO you're running on the low end side of the HP needs of that hull and you have an issue with your prop. I ran a hull of similar weight and style (Grady 204C) with a Merc 175 on it for a several years. With the 175 Hp I was running 14 x 17 Stilletto SS prop on it. The boat was responsive and getting the butt up and out of the water was never an issue. I could not imagine running that boat with 25% reduction in HP let alone a 14 x 19 prop.

If your cruise speed is 27 MPH @ 4K as you say, you're looking at 25% slip. Even your WOT 5.3K RPM@ 42 MPH is on the high side. I would play with props to get your slip back within reason before I spent the money on tabs.
 

jdlough

Master Chief Petty Officer
Joined
Jul 15, 2006
Messages
824
Re: Will trim tabs expand operational cruising speeds

dingbat,

I kinda, sorta, not-quite disagree a bit. Just in the 'bang for the buck' area.

His 14X19" prop at WOT is 5300, so it's almost there (assuming 'there' is 5500). So a shiny new 14x17 might be better to get to that number.

I think a bigger bang for buck is to keep the same prop, and add Smart Tabs for $100. He WILL get on plane sooner, WILL stay on plane at a lower speed, and (to judge from my boat) his WOT RPMs will increase. (Plus other benefits discussed on this forum ad nauseum)

I have a SeaSwirl 2100 DC with 175HP Johnson. Previous WOT @ 5200. Added Smart Tabs WOT is now about 5600. I suspect because the boat's pad is smaller (the whole boat is a bit further out of the water). And I don't really 'drop off' plane anymore. It feels kinda like I 'ooze off' plane. It's hard to tell, it's so smooth, but I feel like I'm still on plane at around 16-17MPH GPS. Tubing kids at low speeds is way easier now, for all concerned.
 

chriscraft254

Commander
Joined
Jun 4, 2011
Messages
2,445
Re: Will trim tabs expand operational cruising speeds

Get the trim tabs you will be very happy you did. But learn how to use them properly. They will increase just about every part of the performance numbers on your boat. Bennet, lenco or smart tabs. I'm running smart tabs and it was the best upgrade to my boat. Any stern driven boat imo should have trim tabs.
 

Bamaman1

Lieutenant Commander
Joined
May 15, 2011
Messages
1,895
Re: Will trim tabs expand operational cruising speeds

A set of hydraulic trim tabs is the best $400 you'll ever spend on your boat. That way, you can greatly lower your planing speeds.

Best thing is when a couple of fat women sit on the same side yapping, you can adjust the boat to where it's level.

I usually leave my power trim at the optimal level--just a tap below a gentle rock. Then, I'll use the trim tabs when accelerating from a stop, when I want to go slow (sightseeing) and when I come up on a big, gut jarring white cap.

Trim tabs make your boat pull like it's got 30 more horsepower and it makes it ride like it's 5' longer--when you tuck them down. They're easily installed by a non-mechanic, and they're a great value for what they do.
 

bobdec

Petty Officer 2nd Class
Joined
Aug 12, 2010
Messages
170
Re: Will trim tabs expand operational cruising speeds

My engine specs on the 1996/150/merc engine is 5000-5600 max RPM, so I felt my prop holding me at 5300 was a safe setup @ 300 RPM below max. Also the plate on this rig says max HP 150. That leaves me at max HP and pretty close to max RPM, so there is very little wiggle room in the power department, except for maybe a specialized prop setup. Think I'm going to go try out the tab route, last two boats I had tabs on were Bennitt's, so thinking they will be my selection. I'll revive this post after install with planing speed and RPM numbers, hopefully positive data. Thanks for the input, appreciate the good info provided by fellow boaters in this forum... Bob D.
 
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