"Rocket" Hydroplane Build

[sean-nós]

I got close enough to 12 using a 13x13 prop with a little bit shaved off the tip and I had to make my own strut If it didn't work out I was also going to go with this transom rudder.

[Sea-Jay]

Dan,

I've got the "Boat Builders Annual" which features Rocket; my dad and I built the 9ft pram dinghy Kingfisher from it in the 1950s

The cover is missing so I do not know the year and there doesn't seem to be any reference to it but from the cars I would say late 1930s or 1940s

Don't be misled by the horsepower quoted, they were measured differently in those days - in the day a suitable engine would probably have been a Ford Flathead V8, which would probably only be described as 40 HP but would still push the boat to a good old lick even by today's standards - they were used by Vospers in their RN "Fast Motor Dinghies" (it would also be a nice period piece!)

[Sea-Jay]

Dan,

I've got the "Boat Builders Annual" which features Rocket; my dad and I built the 9ft pram dinghy Kingfisher from it in the 1950s

The cover is missing so I do not know the year and there doesn't seem to be any reference to it but from the cars I would say late 1930s or 1940s

Don't be misled by the horsepower quoted, they were measured differently in those days - in the day a suitable engine would probably have been a Ford Flathead V8, which would probably only be described as 40 HP but would still push the boat to a good old lick even by today's standards - they were used by Vospers in their RN "Fast Motor Dinghies" (it would also be a nice period piece!)

The clinker built ones are the Fast Motor Dinghies - I think you'll agree they're not hanging about!

http://www.britishpathe.com/video/water ... fast+boats

[solitaire]

When it comes to it -- With any inboard installation it's always worth offsetting the rudder post just enough to get the shaft past the rudder - (it saves al the flaffing around dropping the rudder to remove the shaft) and doesn't make a jot of difference to the performance or handling - (even at 50mph plus)

[water_buoy]

I've been reading a bit about rudders and thought about setting it to one side (slightly) or maybe even slotting the holes in the transom bracket so that it can be tweaked from side to side an inch or so? Also am I right in thinking that an offset rudder can help to counteract the torque effect of the prop direction and make the boat turn the same in both directions?

Re the engine I don't think I'll be going as big as V8 I know some will be disappointed not to see (and hear) one in there but it's going to be heavy and thirsty, plus I don't think I could handle fergals 65 mph speeds I'm not that much of a speed freak (yet).
I'm going to go with a ford straight 4 either the crossflow or pre crossflow engine as I think that should push it along quite nicely and be a lot lighter than a V8.
Sea-Jay when you say they were measured differently in those days do you mean they were putting out 40hp in today's terms or probably more than that?

[Sea-Jay]

Sea-Jay when you say they were measured differently in those days do you mean they were putting out 40hp in today's terms or probably more than that?

They tended to describe engines by horsepower, often using 1000cc per horsepower. ALSO don't forget as far as a boat is concerned it is largely the torque that does the job rather then raw HP (HP is only (torque x RPM)/5252) after all). I am fitting a Ford crossflow into my Albatross with a Kent 224 High Torque camshaft, which reputedly increases torque from 1000 to 6500 rpm

[Sea-Jay]

Sea-Jay when you say they were measured differently in those days do you mean they were putting out 40hp in today's terms or probably more than that?

They tended to describe engines by horsepower, often using 1000cc per horsepower. ALSO don't forget as far as a boat is concerned it is largely the torque that does the job rather then raw HP (HP is only (torque x RPM)/5252) after all). I am fitting a Ford crossflow into my Albatross with a Kent 224 High Torque camshaft, which reputedly increases torque from 1000 to 6500 rpm

Sorry!!! I meant 100cc per HP!

[water_buoy]

Ok so a 1600 crossflow would have been rated at about 16hp and a 4.5 litre V8 would have been 45hp? Seems like they were quite under rated in those days!

[se7en]

I think people are getting horse power and brake horse power mixed up, horse power used to be calculated by a mathmatical equation along the lines of bore x stroke x number of cylinders, devided by a figure something like 2200ft lbs , times efficiency, (God knows how you work that lot out..!! ) this gave those big engines there small horse power ratings, modern engines are Brake horse power rated, this is a crank shaft rating of how many horse power it would take to stop the engine at maximum power,this is what a dynamometer is used for testing , it all depends on what publication your reading and when and where if was written as to what the writer really means, anything written before the around 1950 will most likely be on the old horse power rating, anything after that will most likely be Brake horse power.

[Sea-Jay]

I think people are getting horse power and brake horse power mixed up, horse power used to be calculated by a mathmatical equation along the lines of bore x stroke x number of cylinders, devided by a figure something like 2200ft lbs , times efficiency, (God knows how you work that lot out..!! ) this gave those big engines there small horse power ratings, modern engines are Brake horse power rated, this is a crank shaft rating of how many horse power it would take to stop the engine at maximum power,this is what a dynamometer is used for testing , it all depends on what publication your reading and when and where if was written as to what the writer really means, anything written before the around 1950 will most likely be on the old horse power rating, anything after that will most likely be Brake horse power.

Got it in one Clive!!

The 100e engine in our early Albatrosses came out of a Ford 10 Horsepower Car!