I have recently purchased a 1983 H34' &I'm curious as to what maximum hull speed is. I have perused this site & understand that the H34' is a competetive boat,wich exites me no end because I do plan to race. I look foreward to the responce to this inquiry.
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Rule-of-Thumb algorithm
The rule of thumb algorithm to calculate hull speed is as follows: HULL SPEED = 1.34 * SQR(LWL) where: LWL = Length of water line
The rule of thumb algorithm to calculate hull speed is as follows: HULL SPEED = 1.34 * SQR(LWL) where: LWL = Length of water line
check the specs
In "The Boats" page on this site you will see that the hull speed for the h34 is 7.1 knots.
In "The Boats" page on this site you will see that the hull speed for the h34 is 7.1 knots.
No such thing as "maximum hull speed"
Hull speed is the speed of a wave whose length is the same as the boat's waterline. Paul Akers gave the formula for this. It does NOT define maximum speed for a sailboat. Many sailboats will exceed hullspeed for extended periods of time, even without planing or surfing. Catamarans sometimes do this by a wide margin. The force required to move a boat through the water takes a sharp upward bend as speed increases. For most monohulls the elbow in this curve is near hull speed. But it is a "soft wall," not a sharp limit.
Hull speed is the speed of a wave whose length is the same as the boat's waterline. Paul Akers gave the formula for this. It does NOT define maximum speed for a sailboat. Many sailboats will exceed hullspeed for extended periods of time, even without planing or surfing. Catamarans sometimes do this by a wide margin. The force required to move a boat through the water takes a sharp upward bend as speed increases. For most monohulls the elbow in this curve is near hull speed. But it is a "soft wall," not a sharp limit.
7.8 knots when hull speed is supposed to be 7.1?
What's the deal, was I actually going 7.8 or do I need to recalibrate my speed indicator? According to the specs, my 35.5's hull speed is 7.1 but we were sailing a solid 7.8 on a screaming reach last weekend. How fast should I be able to get the speed up to on my 91 35.5?
What's the deal, was I actually going 7.8 or do I need to recalibrate my speed indicator? According to the specs, my 35.5's hull speed is 7.1 but we were sailing a solid 7.8 on a screaming reach last weekend. How fast should I be able to get the speed up to on my 91 35.5?
Brent: I have a new 340 and by my GPS have exceeded 8.0 knots (screaming is right). Hull speed is nebuluous at best because at a high enough speed most hulls will plane. Your boat's knot meter is only an indicator at best, it records your boat's speed relative to the water. Thanks!
How about current?
Assuming that your speed indicator is properly calibrated, you will more often than not still see a difference in speed between the GPS and your boat speed indicator due to currents and tide movement. In Long Island Sound it can be a little as 1/2 knot up to 3 or 4 knots depending on where you are. MPJ
Assuming that your speed indicator is properly calibrated, you will more often than not still see a difference in speed between the GPS and your boat speed indicator due to currents and tide movement. In Long Island Sound it can be a little as 1/2 knot up to 3 or 4 knots depending on where you are. MPJ
you'll know...
...when you're exceeding hull speed, because you'll start throwing a little rooster tail behind the transom. the bow comes up a bit, the stern settles and--viola--you are no longer a 100% displacement boat. on my 410 (hull speed=8.25 knots) the rooster tail becomes quite pronounced at about 9.5 knots. so does the skipper's grin.
...when you're exceeding hull speed, because you'll start throwing a little rooster tail behind the transom. the bow comes up a bit, the stern settles and--viola--you are no longer a 100% displacement boat. on my 410 (hull speed=8.25 knots) the rooster tail becomes quite pronounced at about 9.5 knots. so does the skipper's grin.
It's physics
A displacement boat can only move so fast through STANDING water. This is water without resistence (wind, waves, tide, etc). If you travel WITH the tide or SURF down a wave, you will go faster. This is speed over ground (SOG). I knew a family who was doing SOG of 11.5 travelling WITH the Gulf Stream.
A displacement boat can only move so fast through STANDING water. This is water without resistence (wind, waves, tide, etc). If you travel WITH the tide or SURF down a wave, you will go faster. This is speed over ground (SOG). I knew a family who was doing SOG of 11.5 travelling WITH the Gulf Stream.
34 Speed
With a relatively accurate knot/log instrument, clean hull, stock two blade prop, my 34 pulled 8.4 knots down the front of steep Chesapeake chop in September of this year. Later the same day saw 7.2 to 7.8 knots on a beam to broad reach. It did not drop below 7.2 knots for about an hour. A fellow owner told me his symmetrical spinnaker equipped 34 saw over 11 knots when surfing. I believe these numbers because in flat water, motoring, 7.1 knots seems to be the limit. Have fun!
With a relatively accurate knot/log instrument, clean hull, stock two blade prop, my 34 pulled 8.4 knots down the front of steep Chesapeake chop in September of this year. Later the same day saw 7.2 to 7.8 knots on a beam to broad reach. It did not drop below 7.2 knots for about an hour. A fellow owner told me his symmetrical spinnaker equipped 34 saw over 11 knots when surfing. I believe these numbers because in flat water, motoring, 7.1 knots seems to be the limit. Have fun!
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