Hill Drag 5 Modified arrived

[Cajunhunter67]

Elwood
Is the slow hole shot a 300R Sportsmaster LU issue? Would the TQ LU fix the Hole shot issue? Or is the 300R just a dog out the hole?

I know the TQ master would limit your top end speed and the need for the 300R. Just wondering if the LU is part of the issue.

Don

[Elwood]

TM is the same gear ratio as the SM and I believe with the same prop you would see the same problems. I believe that it is a low end tuning overbite by Mercury. I also need to be clear that the engine is a beast and I love it. Cruising down the boat lanes at over 80 today was a thrill. I am just looking for perfection...lol

[angle iron]

Speaking of drag, remeber, Drag increases with the square of speed. Small increases in speed generate disproportionately large increase in drag.

Wind drag yes, but the faster your boat goes, the less drag on the hull from water.

[Bass Cat Boats]

The TM2 case will improve hole shot over the SportMaster case.

[AggieBass]

The TM2 case will improve hole shot over the SportMaster case.

I'm not arguing, I just don't understand why. If the TM2 and Sportsmaster have the same gear ratio, and given that hydrodynamic drag is minimal at low speeds (we are talking hole shot, so speeds are from 0 to 25ish); why is the TM2 better? I'm assuming there are other differences than just the lower unit outer surface shape and water pickup location.

BTW - Love your posts Elwood!!! Very interesting work.

[Elwood]

I would not argue with BCB either but have the same question. In the low end side why would one be better than the other beside the pitch prop difference that you can turn with the different lower units. Because of my SM i can reasonably turn a higher pitch prop than a TM because I can raise it more. Problems are with the higher pitch then you get a slower hole shot. A Eyra running a 25 Fury at 3.0 below pad with a 250 XS will be a rocket and will get you in the high 70s to low 80's. Same engine with a SM will turn a higher pitched surfacing prop to the same rpms and be 2-4 mph faster but have a slower hole shot. I picked my boat and motor because I was willing to play with it and have enjoyed it to this point. Finally settling in on a couple props and will continue my quest. There is also so much to explore.....I'm not scared....lol

[Cajunhunter67]

I remembered a thread about the TM having an improved hole shot over the SM. I don't understand the physics difference that would come into play. That was the reason for my question.
Otherwise, I'm enjoying the updates from you on your quest for top end speed, and a perfect balance of overall performance.
Enjoy it and keep it safe!

Don

[crank68]

The TM case also creates more lift that a SM case....

[Bass Cat Boats]

D R A G.

[Rebel1]

The TM case also creates more lift that a SM case....

^^this^^

The SM is designed for hulls that don't require a lot of extra lift whereas the TM is designed to help lift a heavier hull. I think the Erya is a hull that is almost borderline. So would a coned TM on a 300 be the better option?

[Rich1]

Wind drag yes, but the faster your boat goes, the less drag on the hull from water.

Yes, but the drag of the hull that is in the water most likely will be the same or a little more. Drag of the air moving under and around the bottom increases as well as induced drag over the top of hull/engine. If you have done any aeronautical engineering and designed/built a couple of home built airplanes, you will easily see the problem. Does Drag Increase with Speed? As an aircraft's speed increases, drag on the aircraft generally increases much faster. Doubling the speed makes the airplane encounter twice as much air moving twice as fast, causing drag to quadruple. Drag, therefore, sets practical limits on the speed of an aircraft or boat. Water behaves exactly as air does.

[Bass Cat Boats]

Actually the bulk size of a Sportmaster case reduces hole shot as it has more drag. The raising of the case (Engine) elevates it above the water to where the actual prop shaft may be on top of the water line. Almost all of the bullet can be out of the water when approaching higher speeds, thus the drag is reduced by less wetted surface area.

It’s like a ballistic coefficient on small and large bullets, which small bullets are faster and longer bullets can be a totally different coefficient. Water acts much differently than air and the drag situation changes as air reduces the drag in comparison to water. It’s complicated though that’s some fundamentals.

[John Jackson]

Agree water acts much different than air. Air formulas don't work. Water is not compressible. And when you get below approximately 1 inch, it's a totally different set of rules and equations for aero. The faster you go, the more aero affects speed. Almost zero affect on holeshot.
I will add that stern lift with a surfacing sporty provides a lot more stern lift than a subsurface lower.
I'm not an expert, but I did spend 2.5 years at Ga. Tech with aeronautical engineering as my major. And it helped with speed and high speed handling of my race cars.

[Bass Cat Boats]

No, we definitely didn’t mean to infer you weren’t accurate on the air and water situation and vacuum effects as well as other effects on surfaces. There is more drag in a gearcase on hole shot from to larger bulk and design variation than people think. We have run dozens of different cases and some of the things we learned within the last few years shocked us. We have even see gearcases have increased pressure on the steering through the steering wheel just sitting idle. It is shocking some to have learned of what we’ve seen through the recent V8 engine project that none of us expected to learn.

[Mikes250r]

I have a Bass Cat question. When you guys are having hole shot problems is the motor over-revving/blowing out or is the prop biting too much and not getting enough rpms? Cause it seems if it wasn’t getting enough rpm’s vent holes could be added. Just a thought...

[PMantle]

The only hole shot issue I have had was too much vent on a large tube Trophy. When I say problem, I mean the boat would not get on plane at all. As soon as I plugged two holes, that issue was gone.

[Elwood]

I saw some of what Bass Cat is talking about this weekend. I finally bit the bullet and bought a Max 5 ST. I can top the Bobs out and never lose bite. That is close to 2 inches above pad. The bobs scale goes from 0-6 and at about 5.2 on the scale it just lets go and at 6 it is still very hooked up. 4 extra MHP in just a couple seconds after you get past 5. I also discovered that you better Damn well lower the motor from that height before you let out quickly. Had a little bow steering from that oversight....ONCE. The Max 5 ST is a cool prop but still experienced a slow hole shot even with a 27 pitch. Slip numbers are great!!!!!...and the mid range was fun. I did not have a good area to stretch it out but was able to pull 85 and some change at 6000 rpm so high 80's will be achievable with some good water and cooler weather. Water temps were 92 plus and air temp was in mid 90's. I guess unless a magic prop pops up I will have to deal with the slow hole shot and catch people down the lake....lol I tried taking out the vent plugs one by one and really had zero effect on the hole shot. I also have a few more options on the table.....hang on, I am going to get this ironed out.

[shapfromla]

Elwood, It seems as though the Eyra is on the Edge of needing a sportmaster or not. Would you even consider swapping the sportmaster out for a Tourquemaster Gen 2? Not knowing anything for sure I would think the Gen-2 would give you low to mid 80's and not have to worry about the propping issues that you are dealing with on the Sportmaster. Of course this is all just speculation from me since I've never been in an Eyra with a 300 at all. Just a thought.

[Elwood]

Elwood, It seems as though the Eyra is on the Edge of needing a sportmaster or not. Would you even consider swapping the sportmaster out for a Tourquemaster Gen 2? Not knowing anything for sure I would think the Gen-2 would give you low to mid 80's and not have to worry about the propping issues that you are dealing with on the Sportmaster. Of course this is all just speculation from me since I've never been in an Eyra with a 300 at all. Just a thought.

Shap....really not an option for me and I knew what I was getting into and also advise others on the options when I get asked. As for me I like the challenge and the the TM is not rated over 85 mph. SM was the only option. I still have several options as far as props go so I will continue to chase a good tournament prop. I do have several more options for the speed runs this winter......the saga will continue