Bow too low on plane? Problems with ploughing/swerving at WOT.

[Nos4r2]

Been out this weekend and while I have full control in 3'-5' seas I seem to have a problem with the bow ploughing while on the plane at WOT in calm water. It's quite worrying as she swerves all over the place and is almost uncontrollable. I'm also 6mph slower on GPS in calm water because of it.<br />She's fairly heavy at the bow anyway as there's a fair bit of stuff stowed under the bunks in the cabin. <br /><br />I have hydrofoils fitted to the motor and they don't seem to be getting out out the water at WOT when it's calm. I'm wondering if they aren't lifting the transom too much causing the bow to plough. Gonna take them off and try without them anyway. I WAS going to buy some smart tabs but I'm wondering if it's a good idea now as the bow appears to need to lift. I don't have PTT either. Not sure if manually trimming up is a good idea as it looks too much the next pin up.<br />Anyone got any ideas?<br />Here's a picture of an identical hull.<br />

 

[b.gagnon]

Re: Bow too low on plane? Problems with ploughing/swerving at WOT.

What hp motor do you have and how big is the boat?

 

[Nos4r2]

Re: Bow too low on plane? Problems with ploughing/swerving at WOT.

sorry, shoulda posted that. 15'11 and 50hp merc blueband.

 

[stevens]

Re: Bow too low on plane? Problems with ploughing/swerving at WOT.

I'd say probably the hydrofoil is giving you too much lift at higher speeds. Take it off and see how you do then.<br /><br />If you then want a more stable ride, smart tabs might help. They have the advantage vs. foils that they ease off on the lift once they've retracted. You can then trim the bow up or down using the motor trim setting, and the tabs act like a suspension, giving you a more stable ride at all speeds.

 

[Nos4r2]

Re: Bow too low on plane? Problems with ploughing/swerving at WOT.

yeah I was thinking the same about the hydrofoils. I'm not a great fan of them anyway but it was only the 2nd time out with this boat and the hydrofoils seemed to be ok in 3'+ swells-all the calm water was in the no-wake zone on the 1st time out so didn't get to try them.<br /><br />I doubt I'd even have noticed the problem if I had power trim and tilt-but the foils re still coming off anyway.

 

[jamesgreen]

Re: Bow too low on plane? Problems with ploughing/swerving at WOT.

check for water between the hull and the floor. My dads boat had the same problem and they found a bad boot in the out drive and it was taking on water with him knowing. The boat took a long time to plane and was pushing alot of water.

 

[Nos4r2]

Re: Bow too low on plane? Problems with ploughing/swerving at WOT.

That's definitely not the problem, my holeshot is only 4-5 seconds onto the plane. The problem's occuring above 15mph.

 

[Jdeagro]

Re: Bow too low on plane? Problems with ploughing/swerving at WOT.

When you run the hydrofoil it will keep lifting the stern as the speed increases. Since you do not have power trim, check to see which hole the bar is in. If it is close to the transom move it out.

 

[KCLOST]

Re: Bow too low on plane? Problems with ploughing/swerving at WOT.

It sounds like you just have a motor height problem. You need to make sure that the hydrofoil is just above the water line at WOT. If you take the foil off, you still want the anti ventilation plate just above the water line... <br />With it too low you are having too much drag created by the lower unit which actually causes the transom to be pushed upward reducing downward force against the water. Without good force on the water your chines aren't keeping the boat stable... This is called chine walking.<br /><br />The above condition will also prevent the bow from getting up properly...<br /><br />Test carefully and<br />Let us know

 

[fishingdan]

Re: Bow too low on plane? Problems with ploughing/swerving at WOT.

Potential causes are:<br /><br />1) Engine trim in conjunction with the fin. You can adjust the running attitude of the boat by adjusting the trim angle of the engine. Without power tilt and trim, you need to find a trim angle that is a good compromise between hole shot and top end operation. It sounds like you have the engine trimmed in all of the way (the prop is closest to the transom). This will give you great hole shot, but will drive the bow down while running. The fin will exagerate this affect. The trim angle is adjustable on the engine bracket. <br /><br />2) While I think #1 is the primary cause, weight distribution is another area to look at. Do you have a lot of weight forward? If so, get creative and balance the weight so that it is better distributed.<br /><br />Running in calm water is where these characteristics are seen. Running in a chop constantly changes the running attitude of the boat. <br /><br />Good luck. If it is any of the above, it is easily remedied.

 

[Jdeagro]

Re: Bow too low on plane? Problems with ploughing/swerving at WOT.

Nos4r2;<br /><br />What you are experiencing is too much stern lift.<br /><br />Although the hydrofoil will help the boat plane like any other additional planning device, they tend to lift progressively more as the boat speed increases. Especially if they are below water level, or at water level. This excessive lift pushes the bow down and induces bow steering amoung other problems. The boat will loose speed and be very sensitive to steering if not worse.<br /><br />Smart Tabs do not work this way. The amount of lift once the boat is at cruising speeds is 35% less than below planning speeds. Aditionaly they do not increase lift as the boat speed increases since the pressure is regulated, and adjustable to the requirements of the boat.

 

[Bondo]

Re: Bow too low on plane? Problems with ploughing/swerving at WOT.

How Straight is the last 5' of the planeing surface of the Hull ????<br /><br />A little bit of Hook in the Hull will sometimes create the Issues you're having...........

 

[KCLOST]

Re: Bow too low on plane? Problems with ploughing/swerving at WOT.

This should be very possible to correct without the addition of smart tabs... And you can still leave the hydrofoil on... It's just a matter of motor height as well as trim and possibly bow weight....

 

[Nos4r2]

Re: Bow too low on plane? Problems with ploughing/swerving at WOT.

Been out to her today-Realistically I can't adjust the motor height by more than about 1/2" without re drilling my transom but I'll jack it by that much to see if it improves it.It's on the 3rd trim pin setting and looks to be about level.<br /><br />There's no hook in the hull (checked) but the foils are level with the bottom of the hull so they are coming off. I've repacked the cabin contents so the heavier stuff is closer to amidships. I had 60 litres of fuel in the tanks at the stern at the time too.<br /><br />Next time I get to take her out I'll see what the deal is then... might even find I need smart tabs after it's fixed

 

[fishingdan]

Re: Bow too low on plane? Problems with ploughing/swerving at WOT.

Also try various engine trim angles the next time you are out. Easily adjusted on the engine bracket (tilt the engine up, pull the pin out and put it back in a different hole).

 

[CATransplant]

Re: Bow too low on plane? Problems with ploughing/swerving at WOT.

Try one more pin setting out on the trim. That might just be all you need to do.

 

[dajohnson53]

Re: Bow too low on plane? Problems with ploughing/swerving at WOT.

The first thing that came to my mind when I read this thread was: If it were me, I'd strongly consider investing in power trim and tilt before anything else. Either an OEM unit or an aftermarket unit. NOt only is trim a basic adjustment that one needs to make, as many have pointed out, but I'd personally also want power tilt, being old and lazy. I would think this is more basic than trim tabs, but that's just my opinion. Consider putting your money into T/T.

 

[Nos4r2]

Re: Bow too low on plane? Problems with ploughing/swerving at WOT.

I live in the UK-it'd cost me more than the motor's worth to set it up for PT&T with rip-off Britain prices D. Why they price stuff so high is beyond me-it's completely ridiculous. No-one's ever going to be able to recommend something by word of mouth that's so prohibitively expensive they can't buy it!<br /><br />CAtransplant, I think you may well be right but there's no way the foils can come out of the water properly at the moment unless she takes off. Next time I take her out I'll try all the combinations I can think of and that have been suggested.<br /><br />Cheers guys!

 

[gutshot grouper]

Re: Bow too low on plane? Problems with ploughing/swerving at WOT.

YOU SURELY DO NOT NEED ANY MORE LIFT AT THE STERN, YOU PROBABLY NEED TO ELIMINATE THE TABS OR HYDROFOIL, WHATEVER ,AND GET SOME OF THE WEIGHT SHIFTED AFT.

 

[Nos4r2]

Re: Bow too low on plane? Problems with ploughing/swerving at WOT.

That's exactly what I'm saying-the foils are slightly too low at the moment and aren't coming out of the water at WOT-therefore probably providing too much lift to the stern.