Hi All, so I recently purchased a second hand outsider 575 with a 135hp outboard. It's porpoising alot a high speeds and especially if I run into low long intervel swell. I probably need to move more weight forward, however I also feel as though I cannot trim my bow down enough. I don't want to lower my outboard further as it seems to be throwing alot of water as it is. I'm also running a mercury vengeance prop 17 pitch. Any ideas will help. Thanks.
Hillbilly, If you feel you can't trim your bow down enough, and the motor is throwing a lot of spray, you certainly don't want to lower your donk. You need to raise it. This should also help reduce/stop porpoising.Originally Posted by Hillbillyfish
How much grip does this prop have? How far can you trim out before it starts to ventilate? And does this change much between a rough day and a calm day?
Take a mate out and check height of A/V plate. Plenty of posts on here lately about this [emoji1].
Cheers
Brendon
Thanks for the reply,
I seem to be able to trim it out a long way before if vents. When u talk about how much grip the prop has I'm not quite sure what your meaning.. I'm finding in the rough as soon as I slow down to a comfortable speed my bow is to high in the air and i'm landed on the middle to arse end of the boat. Maybe the outboard being to low is dragging the rear of the boat down and forcing the front up?? Also I find when I'm doing high speeds in calm water the boat will be okay until I hit the tinniest amount of swell and then off she goes porpoising like crazy until I slow down a bit and settle it out.
I'm going to shift some weight forward, if I was to cut the boat into half there would be so much more weight at the back. Especially being a walk around cab I think it makes it worse (because the cab is further back in boat and therefore forces people weight ect further back. I might try some sand bags in Toilet area up front and also sand bags in anchor well plus outboard up 2 holes just to see how it performs.
Also do you think I should consider a 4 blade prop, Or for an extra $700 just go for trim tabs. I'm thinking the cruise craft would appreciate the trim tabs as I would be able to lean into or away from side swell better. I'm not to worried about top end speed I just want to be able to cruise at 20 knots in sloppy conditions with the v doing its job.
Cheers
ah no stop......
Here we go again...........
A boat porpoises when its centre of gravity is forward of the centre of lift. This is why really fast boats often have a large engine pod. It moves the centre of lift forward without the centre of gravity moving. So if you add weight in the front of the boat you'll almost certainly make the problem worse. Likewise putting the engine lower will cause the boat to trim more which moves the lift aft and makes the porpoising worse.
Step one. remove any crap you've got in the bow especially if you're carrying excessive amounts of chain.
Step two. Jack the engine up. I'd go all the way and then drop it back down a bit if you need to. You might find it still porpoises even with it all the way up. In which case you'd be wasting your time with halfway measures.
Step three. fit a hydrofoil to the engine. In this case think of the foil as the tail of a plane, it works automatically due to its location to offset changing in trim (or attitude) of the boat.
I suspect there was a slight communication issue when Hillbilly posted " I don't want to lower my outboard further as it seems to be throwing alot of water as it is". Personally I took that as I don't want to trim it in any further.
As the lads above have posted - the issue may well be the engine is mounted too far down on the transom. Getting this right may well cure your issues in regard to the porpoising. If once your engine height is correct, you then have a problem with the prop "blowing out" or losing grip in swelly conditions, a different prop will be on the cards - possibly a 4 blade or a large blade 3 blade.
A foil is then an option or a set of tabs. The foil being the cheapest and easiest. The trim tabs providing the most versatile solution.
Okay I just assumed a little extra weight in the bow would help hold in deeper in the water when It was rough. I cant seem to trim the nose of the boat into the water as much as I would like. Other boats I have owned have been heavier in the bow and have seemed to ride better, or at least had the capacity to dig the nose in when the going got tough. I don't seem to have that option at the moment as the boat seems to flighty up front.
Hillbillyfish,
Put a True Tracker Plate on it, and the rig will be transformed.
I can't speak highly enough of these foils.
Go to www.solas.com.au and check them out.
Tim
I had the same on a Cruisecraft 500, the previous owner had put a 25" Outboard on a 20" transom, when i finally got the height right everything was good.
I know some people are devotees of foils, and i certainly believe that they have a role to play.
But before you go throwing foils on, you really should try to address the real cause of the issue, not just the symptoms. And rhere's a fair to good chance that the root cause is an engine that is buried too deep. It all about the physics and angle of thrust.
It is a somewhat chronic problem, as lots of dealers mount engines too deep - typically they seem to do this to avoid possible complaints about props ventilating. But getting the engine height right will significantly enhance the way the boat rides, and can address issues like a "bow up" attitude and porpoising.
So please listen to the people saying to address the engine height issue.
Its not that difficult to lift the engine height yourself with a couple of mates. Using the trailer jockey wheel method. Done it on a few boats, as have many others. If your're keen to give it a try let us know and we will explain how it works. Quite simple, and safe, with a bit of sensible care.
Note to self: Don't argue with an idiot. They will only bring you down to their level and beat you with experience....
Having the engine too low will also make the bow seem light. Imagine your boat when viewed from side on with a pin put through the middle of the boat at the water line. When you apply horizontal thrust at the props the boat will spin around the pin and the bow will lift. Lift the engines and the lever arm becomes smaller so the same amount of thrust wont lift the bow as much.
I will definatly be lifting the outboard. The only thing is the vent/cave plate is level with the bottom of the boat.
You can definitely go higher if that's the case. Mines at about an inch above the bottom, not the same boat as yours though.
On mine I am about 50 mm higher than the V. The Cruisecraft having a plank at the stern rather than a V may well not let you lift as high (Brendon may have a better idea here - pretty sure he has played with props on a bigger one quite extensively). The thing to do is go one hole at a time unless it is glaringly obvious it is miles too low. The longest wait time in the whole lifting process is waiting for the sealant to dry. If you have a compressor and an air ratchet, you can have the whole job done inside half an hour once you know what your doing.
That's not a reliable way to assess correct engine height.
I will probably cop a flogging, again, but ..... Here goes:
The best way to assess engine height is to get the boat onto a medium/fast planing speed, engine trimmed out to optimum, then get someone trustworthy to hold the wheeel while you go down to the transom, look over the back and try to see the cav/anti-vent plate (the largest flat plate above the prop).
If is buried DEEP under water so you cant see it at all, the motor is too deep and should be raised. Especially if currently there is little tendency for the prop to lose grip in turns, following seas etc. so raise one hole, and test again. If still too deep and prop still hangs on real good, you can go up another hole, and then test again.
Now there are some varied opinions on this forum about how this plate should be running relative to the water surface when the boats on the plane like described above. One says 12mm below the surface, many others say generally skimming the surface or getting splashed, others say theirs runs perfectly well when its 12mm clear above the surface.
But I havent heard anyone, yet, suggest that its a good idea for it to be buried any deeper than 12mm under the surface, at least not on a fibreglass offshore V hull like yours.
So its probably safe (i hope!) to say it should be running close to the surface.
Then, once you get it there, things like prop selection and specific hull characteristics tend to be the determinant of the final engine height selected.
(Standing by for incoming.....)
Note to self: Don't argue with an idiot. They will only bring you down to their level and beat you with experience....
By the way, the following describes how I and others I know lift motors using the trailer jockey wheel.
Lifting outboard motors to higher hole - the jockey wheel method.
This method can also be used to lower motors, just adjust which way you wind the jockey wheel.
Doing it this way you dont even need to disconnect anything, (steeering, cables etc) provided of course you assess that nothing is going to foul anywhere during the process. Ive never had to disconnect anything using this method.
Resources required:
- Spanners/socket correct size for nuts and bolts holding engine on.
- You, plus 2 mates, preferably reasonably solid units! No wimps please.
Park boat-trailer on a flat surface and chock the wheels, front and back, so it wont move. Then:
- Trim motor down so it is vertical, maybe just a little bit trimmed out.
- Place a block of solid wood on ground under the skeg. You may need to put some bricks etc under it to make a stable platform, so the block of wood is just 1 or 2 cm below the skeg.
- You go to front of trailer and wind jockey wheel up - this means that the engine lowers at the back, so that its weight is now solidly taken by the skeg sitting on the block of wood. The skeg is plenty strong enough to carry the weight of the engine. The wood acts as a cushion.
- Now go back to the motor.
- Loosen off nuts. Your 2 mates are steadying the motor from each side while you do this. Bear hugs. Keeping it balanced is the idea. Not very difficult to do. Just be careful to not let it overbalance.
- Depending on the motor bracket, you might have to take the top bolts all the way out but may be able to leave the bottom ones in, but with nuts removed or loosened if they are in slots in the bracket.
- Mates now carefully tilt the motor back just enough so the bolts are able to get out and you can scrape/clean the old sika from around the bolt holes and engine bracket.
- You then go around to the jockey wheel again and wind it up a bit more, your mates tell you how far to go so the bolts will line up with the new holes on the bracket that you want to use.
- You come back round to the motor, apply fresh sika around the bolt holes and bracket as required, then you and your mates gently tilt/slide the motor back over the bolts and get the nuts back on and tightened up.
Done.
Note to self: Don't argue with an idiot. They will only bring you down to their level and beat you with experience....
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