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pushing on the nose

WELL this past saturday I ordered a 14 by 7.5 hamant hull it's time to up grade then on sunday on my way in I bounced off a cypress tree and cracked my glass hull again so it's back to patching again It takes about 6 weeks for an aluminum hull but I should be happy with it talked to a lot of people about different hulls and they are priced well. http://www.airboatsbyhamant.com
 
Sorry to hear about your boat getting smashed, but congrats on you new one.
Bet you can't wait to get it.
 
I figure that I can fix the glass one and run it untill the new one is done but I still have to rig out the new one and put polymer on it so it will probably be about 4 months till the new is ready can't wait. this time it was one of those cracks that if you are on a plane the water seeped in and if you stoped it pored in so I flew to the boat ramp and did not stop until I got out of the water also looked back and seen that the gorund wire off the bilge pump got knocked off,but made it back and did not sink the crack is about 2 feet long right on the corner .
 
I had another boat aways behind me .My buddy bumped the same tree the week before and threw his wife out of the boat. but we still run around there that was the first time,ran that trail 20 times before but all it takes is one time. did see where some one hit a tree relly hard glad it was not me.
 
CCHardt - Congrats on your new purchase. I am being sucked down that same pipe. It's just money.

Glad you weren't hurt and that you did not contribute to the Brevard Artificial Reef Program.

Bet you were near the same area where FAA ran last month. I saw the same fellow crack up twice on that run. He was driving a friend's deckover boat with a single rudder and watching that boat was enough to cure me of ever wanting a single rudder airboat.

Seems your corner of the marsh offers three great choices for aluminum hulls Hamant, Classic / Alumatech & Diamondback.

What drove your decision?
 
Every car motor ride boat I have owned but one rode on the nose. I owned a Gore, Lewis, Gilleo and a Hawk step hull that all pushed down on the nose. My Hammant hull was the only hull that didn’t. I had two boats that I could floor it and shove the bow cap under water. Almost took a trip to the hospital the first time it happened I wasn’t ready for that. I may be wrong but I have found if you have a car motor boat that rides hard on the nose no amount of jack on the bottom or jack in the motor will solve the problem. These adjustments are only a fine tune knob. I have found 90% of all boat manufactures base all their riggings and hull designs on aircraft motors. The difficult problem to over come with a car motor is the larger 78’’ and 80’’ props raise the motor higher which intern gives the prop thrust leverage to shove the nose down. The other problem is the average airboat car motor now a days makes 400HP this also pushes down more on the nose. After five or six attempts with as many hulls and riggings I’m finally getting were I want to be with a ride boat. I hope my new ride boat does what I want (I think it will). I’m tired of chasing the plowing problem.
 
If you have a good amount of seat time and don’t need a barge to feel safe, I can assure you will be very happy with your Hammant hull. Did you go with a .125 bottom and sides? I built a strong 500HP 406 SBC for a customer that ran a Hammant hull. It was very fast for a ride boat. He actually cleaned house in the ride boat class at the races. The boat handled and rode superbly just like my Hammant hull did.
 
Well, here we go again...

A good friend runs a 16' Alumatech with a 502 / 502 blower motor as a scout boat on several of the professional redfish tours.

His performance issue is severe porpoising at any speed over about 30 mph, not pushing. Go figure
 
That's good for him because proposing is the easiest thing to fix it’s 20 times easer than getting a boat to stop pushing on the nose. His boat is obviously intended for a car motor that’s why it doesn’t plow, not to mention it’s 16 feet long. I have never seen an aircraft motor on a 16 ft boat. Put that 502 on an average 12 or 13 foot hull and it will plow especially if it makes good horsepower
 
Waterthunder, OK, I'll bite. Maybe I can help a friend. What is the easy fix he should try? Still trying to establish direct contact on that possible motor sale for you.
 
Has anyone tried bending the back tab down yet. If not get a large crescent wrench and bend down the lip on the bottom of the boat that sticks out past the transom. The tabs usually stick out about a ½ inch. If you only tweak them a little you can run dry without the tab bending back. So just barely bend the whole tab down. This usually works in it’s self if that doesn’t over come the boats tendency to propose then just bolt on a electric trim tab so you can adjust it as you ride. I will Email you tonight over the motor. I have sold three motors this week and I’m trying to have one ready for the test stand on Friday. I’m sorry about not contacting you I have just been under the gun to deliver some of these motors.
 
bigdaddy I talked to alot of people and most said hamant or alumathec they build there hulls like a fiber glass hull with round sides and a chime plus I had a 0480 and hamant traded for a new hull.so no money out of pocket.


Waterthunder don't know what thickness yet will be there on sat to talk more about it been running my boat for 3 years but just put a rotator and prop on about 3 months ago but you can only put so much in a 11ft 8in hull
 
When you go to Hammants on Sat I may see you there. They are working on a hull just like yours that I built a 500HP 406SBC for around 4 years ago. Their adding rod boxes and a platform to it. It is one of the funniest boats I have driven. I’m sure you will love yours.
 
I can't wait to get it I saw the boat your talking about. I have to get some measurements so I can start building new rigging for it.
 
a prop will act like a gyroscope, if you shim up the prop end of your engine it will seek natural center thus lifting the bow if you lower it will push the bow down causing it to plow.
 
Dave touched on something a few posts back in this thread that is dead accurate. The reason big motors try to get on the nose is because they use a higher engine stand putting the motor higher for a longer prop.

The thing is this. To run dead level the center line of thrust must be equal to the centerline of drag. This is an age old delima with anything that uses a pusher type motor.

You dont want to know how many people have been killed in gyrocopters that have a high thrust line. Its deadly. The best solution so far in Gyros is a tractor design. Others have changed the centerline of drag by moving weight higher in the craft. Unofortunately you cant change where the water is in a boat hull.

What you CAN do is run a shorter prop and add pitch. Its a tradeoff delima, some claim ya lose thrust anytime ya shorten a prop, and ya can't get it back by adding pitch. All my car motor boats ran a 70 inch prop and I had some that were more neutral handeling with a 68' prop. I personally liked the small amount of nose riding, it made the hull handle much quicker but it did set ya up for countersteer in fast corners. Had I ran longer still prop the nose down issue then would have then become a problem instead of an advantage.

There never will be a one size fits all. As far as I can see this issue will always be a tradeoff between centerline of drag and centerline of thrust.

EDIT: Another issue is the transverse center of ballance -vs- the transverse center of lift of the hull. This is why some hulls handle so differently from others. With a hull, you cant change the designed in transverse center of lift, but you can tune it with jacks or trim tabs (at certain speeds). You can also greatly change the transverse center of balance. Anyone who flies a plane knows this balancing act for every flight. In airboats it is essential to locate the transverse center of balance then work forward or aft from that when balancing a hull out.

Tabs and jacks are modifiers and if at all possible the boat should be balanced to use the minimum of either to run the way you want it to without porpoising. When you set up a hull to handle quickly you are destabilizing the balance if you set it up to handle slow you are stabilizing the balance between all these factors. Some hulls/boats are just easier to set up than others because of the designed in location of these factors.

Scotty
 
c chardt":1g11emd5 said:
you mean try rasing the rear of the motor so it will lift the front. if i raise the engine stand it will probably help push better because the prop is about 4" from the bottom of the boat and that means that the prop is about 12 to 14 in down inside the boat and about 2" away from transom. so if i tilt the engine the prop might hit the transom. still need a bigger hull.

I had the same problem. Turns out I had a 72" prop that went about 18" below the transom. So the prop was not pushing evenly from top to bottom. Too much push from the top and the air flow on the bottom was blocked by the transom. I had to either go with a much shorter prop or build a new motor stand.

Geoff
 
hmgm .... there's another option. Add more propeller blades. If you're farther below the transom than you want to be, go to a shorter prop that seems to fit better and add a blade or two.

It's less money than new riggin and prop cages and you will have more push at cruise. 18" is a lot though.
 
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