Boat lists on the plane

Patrick

Sealiner
Hi all,

When my Wiltblitz gets up on the plane, she tends to suddenly list sharply to either side at high speed. Pretty frightening as it feels that she's gonna flip and you have to back off with the throttle.

The skipper i was running with on Sun says that she is very sensitive to trim adjustments, and after some tuning he got her to sit properly on the plane. He suggested that i put special fins on the motors to correct this, instead of having to rely on over sensitive trimming each time.

Because there is a wealth of experience here on SL, does anyone recommend me doing this? He said it is something i can fit myself.

She is powered by 2 30hp and one boat shop said thats pretty big power for a Witblitz. Could be the overpower causing this?

Cheers in advance.
 

Hammertime

Sealiner
The fins "Dolphin fins I think they called them" should hold her stern down and certainly stabalise the ride somewhat. We used to fit them to the rubber ducks we used as lifeguards. They kept the stern down a lot.

Patrick, there is a guy here in Cape Town, Bruce Williams - Offshore Marine.
I have posted his details on SeaLine before and he has helped a member out.

Please give him a ring and I guaranteed he will be able to help you with minimal effort and cost, before you go buy anything.
Bruce consults to major boat builders nationwide and has great knowledge in this area.
Bruce - 021 786 1007
 

Patrick

Sealiner
Nice! Thanks HT, will give him a call.

Seen these on the net...
 

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Patrick

Sealiner
Spoke to Bruce, says these are waste of time. Wont make any difference and have a tendacy to snap off. Suggested i put racing props on at R2700 a prop. Think i'll just get very good at trimming my motors for now thank you.
 

trevz

Senior Member
hi patrick

why did bruce suggest you put on racing props, i mean how would that help you.

trevz
 

Patrick

Sealiner
He says because the motors are overpowering the boat its causing cavitation with the motors trimmed down. With this, as the one motor then cavitates out of the water and back in, it will bite and cause the boat to push to one side and thus list, with the danger of broaching. The racing props he says will give better "grip" and thus reduce this.
I'm gonna just work on my skills at getting the motors trimmed up correctly as was achieved on Sun by the skipper. Once it was there, this movement stopped. Its gonna take a bit of practice i guess.
 

carcharias

Sealiner
If you are running 3 blade props, try a set of 4 blade props .
4 blades may solve your problem. Try get a set to test before spending huge cash for nothing.
 

Mombakkie

Senior Member
Also .....your motors may be mounted too high on the transom. Because you running a cat-hull the effects of this will be more pronounced.(When you trim make sure to trim the motors "in" or "out" evenly i.o.w same amount of trim.)
The boat may be overpowered... in which case just dont trim the motors out too far. Remember in a big chop its better to run with your motors trimmed "in" so the hull runs through the chop and not over the chop, when its flat you can trim out, when you feel listing or chine-walk then trim back in a bit. Also have a look at the way your gear is stowed about the boat, better to have the weight evenly distributed and as far back as possible.

Playing around with props can lead to you motors running at too high revs (not good for the motor) and props dont come cheap.
 

Mombakkie

Senior Member
Another thing ... the fact that you can reach high speed means you cant be cavitating too badly. If you cavitate you lose speed, obviously cavitation isnt good because there's no water round the prop and no water at the intake for the water pump so your motor can overheat if it cavitates for long periods.

So jus trim in a little and sacrifice a few km/h and you'll be sorted.

You rig is probably overpowered a little, ideal motors for a witblits probably 20 - 25 hp. But having the extra power when you need it is a good thing, makes negotiating rough water a bit easier.
 

miles

Sealiner
Hiya

I owned as witblitz with 2x30hp mariner/yamaha 2 cylinders for more than 6 years. Great little boats!! My motors were not trim and tilt. So, i simply left the motors on one setting. Unfortunately, i can't remember what it was!!

Hydrofins, like Doelfins and Stingray work well, when you need to keep the boats nose down. It also extends your boats length, effectively making your boat longer. I fitted one to my 5.0m gemini as well as to my 4.3m gemini. Worked well on both boats. I how-ever don't think that they'll help in your situation. They also cost R800-R1000 each!!

Since trim settings fixed the problem, your solution is easy!! Get used to the boat!! Take a knowledgable skipper out and spend a day getting to know your boat. I've seen many witblitz's and none of them had hydrofins on. The cavitation due to overpowering is simple to resolve, just open your throttle slower!! Another thing worth doing is going out on a flat day with your gps. Set your boat at a speed that you're happy with, say 20knts. Now slowly adjust the trim and then run the boat watching the speed on the gps. You'll soon find out exactly WHERE the boats speed is the highest. This will be your 'sweet spot':D:D

Some tips for the witblitz. Its a small boat!! REMEMBER that!! In a rough sea, she bangs alot and is wet!! When the sea picks up, SLOW DOWN!! Even if it means you're not getting onto the plane. A boat banging is detrimental to its occupants as well as the vessel!! Another thing worth doing is raising your transom. Just fibreglass or even nail/screw in a peice of plastic or wood on the transom, between the two motors, maybe 20cm high. On anchor, or when drifting, she has a tendency to slop some water over the transom. Unfortunately, there is very little space for a motor well, so i built my transom up. Took me less than 30 minutes, complete with flow-coating it

One last thing: when you came off the water, with the boat back on the trailer, was there alot of water in the hull? Did lost of water come out of the bungs? If yes, did one hull have alot more water than the other?

Regards

miles
 

Freakazoid

Senior Member
Pat, to add to the questions. It seems your boat was listing when the motors were trimemd down and it improved when you trim them up, right? If so the you might have some bow steer. It generally happens at higher speed when the bow is digging in. A shorter boat with a deep front end does that if the bow is trimmed into the water. Basically the front end digs in, the water on the inside of port hull seperates due to hitting a swell or whatever, then there is no resistance and the boat will veer to the right due to water pressure on the outside of the port hull. It can be quite sudden and harsh. It is almost the same effect as an airplane wing stalling, just that it happens in the vertical plane on a boat.

Monohulls with deep V's like the Robbies tend to do this as well when in a following sea. Trimming up will alleviate this. I assume you trim the motors right donw when climbing onto the plane and then trim out. Try setting your trim as Miles said and then just don't go lower than this unless your props start climbing out the water in rough seas, in which case you should slow down anyway.
 

Patrick

Sealiner
FZ thats exactly whats happening - you've explained it better than me. The bow tends to dig in as you've described. Thanks

Miles, i agree, i think its just something i need to get practice on and get to know the boat.Skipper got her to run properly on Sun so i must just achieve that again with the trims. Its just a matter of getting my head around whats taking place at each given moment.

As for the speed aspect, i like to play it safe so definitely no gunning it in rough seas for me anyway.

Thanks to ALL of you for the damn good advice!! If we can get out this weekend, then i'll let you know how it went.

Cheers
 

orange

Senior Member
My two cents worth, my old man has the same boat, same 30hp engines. He has fins and no problem. Funny enough the boat came from being won at a competition, directly from agents with the fins on. Go figure!
 

Patrick

Sealiner
Interesting Orange. The skipper i was with swore that i must get them, yet Bruce from Offshore Marine was dead against them. Said they're a waste and will break easily.
 

dugongboy

Sealiner
I have a 14'6" ski vee with 2 x 25's with fins and they are great - 9years - no problem.
I also cannot beleive that 2 x 30's are too powerful - rubbish - just apply the power in moderation - generally a motor is only a problem if it is too heavy, thus unbalancing the boat. You have to play around with the trim adjustment an see what works best, remember conditions vary from day to day and even hour to hour, also the positioning of your crew is vital on a small boat, also remember small cats are known to get unstable when pushed hard in the bumpy stuff especially when going 3/4 into it so just reduce speed for safety.
 

miles

Sealiner
Hiya

Don't know if this holds any bearing, but the 430 Witblitz were built by a company called SuperCat, owned by Dennis Schultz. They also make the 520 supercat and the 530 supercat as well as the 620 supercat, all in various configurations. A while back, Supercat sold the moulds to SupremeCraft. They now make the boats. Supercat now pretty much only concertrate on their larger displacement hull vessels.

Many years back i spoke to the owner of supercat and he reckoned a very good set-up was actually 2x15hp motors of a 430 witblitz!!

Not thats any of this actually helps, just thought i'd mention it!!

Regards

miles
 

Patrick

Sealiner
True Miles, that is the history. They're in Port Alfred.

Right, time for this wind to drop so i can put the theories to the test.
 
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