Hydrofoils ?
Guys after 3 trips out in the new boat starting to get used to how it handles, but having difficulty with maintaining speeds. 5.5mtr Runabout with Johnson 130hp 2 stroke V4 motor.
I'm either just pushing through the water and possibly chewing juice no end, or if I attempt to throttle forward to pick up even a bit of speed, and start to get up onto even a bit of a plane, the boat virtually without me even touching the throttle any further, just increases both speed and revs and just begins to take off and get quicker and quicker, until I back the throttle off, but when I do that the boat virtually comes to a standstill, mind you this is trying to keep to river speeds.
I went out with a mate in his boat on the river on Saturday and he said my bow was sitting up out the water a lot, but no matter how much I trim it I don't seem to be able to keep it down in front under power.
My mate suggested a Hydro foil or Permatrim.
What are your thoughts and suggestions ?
till
Posts: 9358
Date Joined: 21/02/08
Lots of content on foils in
Lots of content on foils in search.
I don't much like them myself, they can make your boat a bit scary in a following sea.
Dan
Posts: 168
Date Joined: 23/02/06
maybe some aftermarket trim
maybe some aftermarket trim tabs ?
- extend the 'planing surface' of your hull, and also act to raise the rear of the boat (hence motors)
latest Sport Fishing Mag (US) has a great article on it (can get it on iPad, or some selected newsagents) - great read !
Ours are bloody brilliant ! :)
nev
Posts: 193
Date Joined: 04/02/09
permatrim
worked well on my 6.1metre 2008 Assassin mate. Boat was a pig before I got it fitted. Did wonders also on a 20 foot Stejcraft I had years ago also , but a friend had one on a 5 metre quintrex and it was bloody dangerous, got him to take it off and it handled like it should have. cheers nev
strike_zone
Posts: 403
Date Joined: 09/09/10
hydrofoils are a great mystery
you just dont know how it will handle until you try it some people love them and some people say they are down right dangerous my personel experience on a 4.8m swiftcraft was scary on 3 seperate occasions the boat pulled over on its side to the gunwhale rubber at cruising speed scared shit out of everyone me each time never happened again once it was taken off have you thought of putting transom wedges between your hull and your motor they allow you to get more trim and are a better option
eziliving
Posts: 875
Date Joined: 30/12/09
Pharlap i have got a hydro
Pharlap i have got a hydro foil on mine and works great. i have a 6.0mtr polycraft and the following sea does not bother me as my boat has massive reverse chimes which pretty much holds it straight. i tried for 4months with out it and found i lost a alot of trim and the ride became alot rougher so i put it back on. another option is possibly a 4 blade prop as they tend to lift the arse end out of the water so i have been told. just beware with the hydro foil there is a very good chance that you may lose a couplel of knots of your top end speed.
Get busy living, or get busy dying!
iana
Posts: 652
Date Joined: 21/09/09
Small power boats usually
Small power boats usually have planning hulls. Travelling on the plane, the boat has broken away from the water it was pushing along in front of it, and is now skimming across the surface. Since the resistance that the motor was labouring against has reduced substantially, the motor RPM will increase, and of coarse the boat speed will increase by about 10 knots with out you touching the throttle. You back the throttle off so that its maintaining a plane at a reduced speed, then a wave hits the bow, knocks more speed off, past what the boat needs, to be on the plane and the boat bogs down. Edge the throttles forward gently, and so the cycle starts all over again, I know it well.
The RST workbook has a couple of paragraphs on trim and stability. And before I would fit any external trimming devices, I would look at the balance of the boat. If it is stern heavy then you could consider moving fixed weights forward such as batteries, fuel and other weights such as spare anchors etc. When you move weights about, you are working with moments about the centre of gravity. That is the weight X distance. Just moving a battery/s can make a huge difference. The other thing to consider is the seating of the crew, bring them as far forward as practical.
In an ideal world , at your cruising speed, the centre line of thrust, from the prop should be in parallel with the (I suppose the) surface of the water. That way all the power of the motor is being used to propel the boat forward. If the motor is trimmed forward or back some of that power is being used to lift or lower the stern. Costing fuel. You don’t get anything for nothing.
Same as adding anything into the water causing resistance or drag on the hull will also cause more petrol to be used. I would work on weight and balance first before spending money else where.
pharlap
Posts: 69
Date Joined: 02/01/12
Shifting weight then...
All good advice guys thanks, looks like a bit more homework needs to be done before a final decision on external ad ons.
If I look at trying to redistribute weight, maybe this could solve another issue, because I want to move my fuel tank from its current position sitting on the floor, at the back of the boat right in front of the motor, It's a 67ltr tank that full is bloody heavy.
If I was to move the fuel tank up to the bow area, I have an area between say the windscreen and the nose where you can go up underneath through a trap door to the anchor well.
IS THAT SAFE ? to have the fuel line then running along underneath the gunnel, back towards the motor, with all the electrical and steering cables ?
iana
Posts: 652
Date Joined: 21/09/09
Idealy your fuel tank should
Idealy your fuel tank should be just forward or at the centre of gravity. This is because the moments are at the least. Lets say you have 100 kgs of fuel when full, but 0 kgs when empty. the boat wont experience any change in trim when the fuel tank is at the c of g. All that will happen is the hull is further in the water. If your c of g is 2 meters from the bow, then a fuel tank at the bow will have 100kg x 2m = 200 moments when full and 0 moments when empty. So are you going to balance the boat with a full tank or an empty tank, either way its a big shift in the balance.
nico
Posts: 226
Date Joined: 17/08/10
This is good avice iana i
This is good avice iana i agree 100 %
In Mocean
iana
Posts: 652
Date Joined: 21/09/09
Thanks nico that makes me
Thanks nico that makes me feel good!
pharlap
Posts: 69
Date Joined: 02/01/12
Update
Well the hydrofoil was fitted, when I went to my local marine dealer they also gave me further great advice, we spent 2 days down at Mandurah testing it inside and out to about 2 miles, and while conditions were minimal I can say my response would be very positive, handled much better, no further reving up and down, biggest improvement was the way the boat levelled out getting the bow down.
Thanks again guys.