Bow dropping at high speeds
#1
Registered
Thread Starter
Join Date: Sep 2010
Location: Long Island NY
Posts: 673
Likes: 0
Received 0 Likes
on
0 Posts
Bow dropping at high speeds
I just finished a project sonic 35 SS, 725 hp bravo drives,28pitch bravo 4 blade props
At cruising speed the bow rides good and reacts to trim as it should. It I trim too much it porpoises , after 60mph the bow begins to drop and the faster I go the more it pushes down. At 80mph the boat is bow steering .
I checked all the usual things , hook in hull, drive alignment .
My last thing to try will be spinning props In
Any ideas?
At cruising speed the bow rides good and reacts to trim as it should. It I trim too much it porpoises , after 60mph the bow begins to drop and the faster I go the more it pushes down. At 80mph the boat is bow steering .
I checked all the usual things , hook in hull, drive alignment .
My last thing to try will be spinning props In
Any ideas?
#4
Registered
Thread Starter
Join Date: Sep 2010
Location: Long Island NY
Posts: 673
Likes: 0
Received 0 Likes
on
0 Posts
The porpoising isnt a problem, just explaining that under 60 the boat carries the bow and reacts to trim , but if I go faster the bow starts to push down and I can't trim doesn't help
#5
Platinum Member
Platinum Member
Does the speed continue to climb thru the entire RPM range? IMO, there becomes a point that the bottom of the boat has more more impact on the attitude than the trim...at least on a straight vee where the hull continues to come further out of water as the speed increases. I am not sure about other hull designs.
Ben
Ben
#6
Gold Member
Gold Member
Some older V-bottoms love the extra stern lift that 4 blade props provide. However, certain 4 blade props on certain older hulls just don't like them at all. I tried a Spinelli 4 blade on mine a few years ago and the handling was downright spooky with way too much stern lift (leading to bow steer at higher speeds) and a really un-nerving tendency to try to paddle-wheel the stern around in turns. My Trophy 4 blade has no such tendencies though.
The first thing I'd recommend is a call to Brett at Bblades to see what the master thinks. In the mean time, I'd try a set of 3 blades just to see what happens.
The first thing I'd recommend is a call to Brett at Bblades to see what the master thinks. In the mean time, I'd try a set of 3 blades just to see what happens.
#8
Platinum Member
Platinum Member
The props can help, but with a hook you will still be scrubbing speed. The trade off with no hook is you just drag the tabs a little in the mid-range. You could be talking a +2-4 MPH w/o the hook.
#9
Registered
Join Date: Nov 2001
Location: Pennsylvania
Posts: 3,385
Likes: 0
Received 0 Likes
on
0 Posts
My panther did the same thing when I added significant power. It was unsafe with bow steer. I tried spinning the props in and whala, the boat raised up out of the water and handled significantly better.
#10
Gold Member
Gold Member
Speaking of which, any time you're running over 65-70 MPH, I always recommend hydraulic steering too.