Real, factual test results for doel-fin

[metriccrescentwrench]

From time to time there have been very emotional discussions on here about the virtues of mounting a fin on an outboard engine's AV plate, with all the usual 'experts' expressing their opinion. A fin is pretty simple in what it does, at low speed it provides a lifting force which helps get a boat on plane quicker.

My Checkmate has a pad type hull, which is designed to go fast. It works well at water-ski speeds, but below around 20 mph or so it starts falling off plane. My kids like to wake-board (at 18 to 19 mph), but a wake-boarding boat just isn't in the picture. For a couple of years I just made do, wallowing on the edge of falling off plane while pulling wake-boarders. Driving like that is a real challenge, and precise speed control is difficult (and of course it's always the drivers fault!). Even with a 4 blade prop pitched for good hole shot, speed control was tough with the boat on the ragged edge of planing. So essentially we're using my boat outside of the performance parameters it was originally designed for (all in the name of fun, of course).

I added a fin this year and it did exactly what it was supposed to. I'm fully on-plane at around 15 mph now which makes speed control at the 18 or 19 mph the kids want for wake-boarding much easier. As for any loss of top speed, if I lost any it wasn't much. With a light load, 1/4 tank of fuel, and my 4 blade hole-shot prop I had a top speed of around 61 mph without the fin. The only time I made a full speed dash this year (with the fin) there were 4 people in the boat, the fuel tank was 3/4 full and I managed 58 mph, so top speed was essentially unaffected (which is what you'd expect, because at that speed the fin is out of the water).

 

[Lager]

Yep, that sounds about right The fin just gives you more mechanical advantage against what your hull wants it to do at that speed.There are more expensive ways to achieve this, like trim tabs and they might work better ? But a fin works quite well for what you are wanting to do with it and helps with prop blowout on sharp turns. Glad it worked out for you.

 

[NYBo]

opcorn: Here we go!

 

[kjsAZ]

Sorry, solicitation......

WIMUSKY

 

[metriccrescentwrench]

opcorn: Here we go!

Yep, I'm waiting.

.....The fin just gives you more mechanical advantage against what your hull wants it to do at that speed.There are more expensive ways to achieve this, like trim tabs and they might work better ?

Exactly. And for the argument that smart tabs or trim tabs would be better, we're only talking about an 18-1/2 ft boat, and at a cost of $40 or so vs. several hundred, and no holes in the transom as an added bonus.

and helps with prop blowout on sharp turns.

I was actually wondering about that, I thought the fin might help with that but wasn't sure. I settled on my current engine height (prop centerline about 3" below the pad) as a compromise because of the prop blowing out in turns. I've got plenty of water pressure to go higher (the top water inlet holes have been closed off). I might just raise the jackplate another half inch or so and see what happens.



Edit to add:

I just realized that I totally overlooked something. The boat used to wander a good bit in the no-wake zones (and I have to go through a long one to get to the main part of the lake - George Thorogood's 'Bad to the Bone' played in its entirety before I made it through). Last weekend with the fin there was absolutely zero low speed wandering. I have a hunch it's because of the design of this particular fin ( http://www.iboats.com/SE-Sport-300-...2848468--session_id.867497677--view_id.168771 ) as I wouldn't expect just a flat hunk of plastic bolted to the AV plate to do anything in respect to this

 

[sphelps]

I guess if it makes for a better boating experience then there is nothing wrong with them . I just don't care for them because they are really ugly . :lol:

 

[WIMUSKY]

I guess if it makes for a better boating experience then there is nothing wrong with them . I just don't care for them because they are really ugly . :lol:

x2...

 

[roscoe]

More like anecdotal evidence.

Yep, they can help.

Unfortunately, most people try using them to overcome a real problem.
A bandaid to fix a larger issue that should be addressed.
Like underpowered, or overweight, or waterlogged foam, or incorrect engine height, or broken trim pump, or incorrect prop, or a combination of these.

 

[kjsAZ]

On some boats/hulls they may help.

My personal experience is different. Last boat (17.5ft, 90HP O/B ) came with a Doel-fin. Measured acceleration (accelerometer) with and then without fin and despite the fact that the boat felt to come up to speed faster with the fin it accelerated better without fin. Current boat (17.5ft, alpha1G2) also came with a Doel-fin PO installed and when first time out I regretted that I bought the boat without a sea-trial. Handled like a drunken sailor and was extremely hard to steer (to much for the admiral to handle) and had a hard time to stay on plane at lower speeds. Took the fin off and she now handles perfect and steers well.

 

[thumpar]

Usually when wakeboarding being off plane is what people want to make a nice wake. The main problem I have with the fin is broken cav plates. They are used on under powered boats or boats that have an issue mostly.

 

[Watermann]

I'm with the increasing the planing surface of the boat crowd as opposed to having the motors AV plate holding up the weight. I would never put one on a stern drive, I just don't like the thought of all the extra force it puts on the LU's gimbal hinge points.

Oh yeah and I forgot, X3 on the're really ugly looking.

 

[JimS123]

Been running a DoelFin (the ONLY brand), for 30 years now on the family boat. Three of my boats have them on and two of my son's boats have them as well. All in all I'd guess 50 years experience total. Never had a broken AV plate and the performance is enhanced on every model bar none.

Oh yes, one even has tabs WITH the fin.....now THAT's performance!!!

ALL of the boats were brand spanking new with all factory equipment and no bubba modifications, so there was nothing "wrong" with any of them.

The Trailer Boats Magazine article (that I posted several times in the past) a few years ago showed real world data and it showed outstanding results.

Ugly is subjective. Personally, if color matched to the OD I think they look cool. If the ugly guy drives a Honda Element we'll give him a pass for saying ugly because he obviously has no taste.....LOL.

 

[skibrain]

Similar goal, i took a different approach. 1989 Glastron CSS-16 (same hull as Carlson CVX) w/ 120 hp outboard. My goal was low-speed plane with a bow-down attitude. I added transom wedges between motor and transom for more negative trim. My 54 mph boat would get up and plane at only 13 mph. Great for what I was doing with my young kids on skis and kneeboard. I lost a bit of trim for running fast, but it was only the last few degrees where it was starting to porpoise.

 

[oldjeep]

Why is it that you want to be on plane for wakeboarding? A wake board boat does everything it can to plant the rear in the water and keep the boat off plane.

 

[Cptkid570]

This is going to sound funny, but I will say it anyway. I think it provides some safety. If I'm parked and someone jumps in off off the back of my boat, or falls off of it, I like that the fin somewhat covers the prop. Or, at least covers it more than the AV plate does.

 

[metriccrescentwrench]

I just don't like the thought of all the extra force it puts on the LU's gimbal hinge points.

What extra force?

Sorry, but that doesn't hold up from an engineering standpoint. A fin will actually decrease those forces because it's providing lift which will partially counteract the weight of the gearcase.

 

[smokeonthewater]

I HAVE personally seen two broken LU's from fins... and while I AM happy the fin worked for you I think to exaggerate the cost of the smart tabs or to insinuate that those of us who have had negative experience with fins are somehow not providing "real factual" information is less than fair to the newby who might be reading this trying to make a decision.... It has been established MANY times here in the IBOATS forums that these fins can sometimes improve performance.... USUALLY (maybe always but I can't say for sure) smart tabs will perform better and while they are more expensive than the less expensive fins they can be had for about the same as the higher priced fins....

Tabs also NEVER cause a boat to handle poorly if installed, adjusted, operated correctly but SOMETIMES the fin does...


In closing...... YES they are hideous but then they are under water when it counts... I WILL say tho that any time I see a boat for sale with one on it I generally assume that it is underpowered or otherwise has performance issues.

ps I have a pretty good stack of these things I have removed from boats over the years... so far I have encountered one boat (alum 14' 7.5 hp tiller) that was better with the fin and maybe a dozen that were better without it... a couple of those (both I/O) were downright dangerous with the fin in place.

 

[kjsAZ]

a couple of those (both I/O) were downright dangerous with the fin in place.

add mine to that category!

 

[metriccrescentwrench]

Why is it that you want to be on plane for wakeboarding? A wake board boat does everything it can to plant the rear in the water and keep the boat off plane.

Yeah, but a wakeboard boat can hold speed easily in that condition. What I was concerned about was just being able to hold a constant speed at the speed kids want to wakeboard (or tube), and by getting on plane at a lower speed I can do that. When my boat is on the ragged edge of planing precise speed control is impossible. I'm not concerned with the quality or size of my wake, I don't have a family of champion wakeboarders so that doesn't matter, but they do complain very loudly when the speed is all over the place.

 

[metriccrescentwrench]

I HAVE personally seen two broken LU's from fins...

I'm guessing what you're talking about is broken AV plates, what someone else was claiming was increased stress on a gimbal bearing. I have to wonder if someone was using the fin as a step or something dumb like that.