speed related to hull size?

[pcrussell50]

it seems like a lot of the traditional mono-hull fastboats like allisons and hydrostreams are what i consider to be "bigger" hulls, like 20 feet. [i have a 16 footer, so 20' sounds big to me]. i and a lot of other knowledgeable s and f folks think i ought to be able to get about 55mph out of my 16 footer, [with a 2.0L 135hp v4 crossflow], and i'm fine with that. but i'm wondering why i couldn't or shouldn't go faster with this hull?

i'm going to throw out some guesses here and you guys can comment if you like:

1] is there something about small hulls that makes them dangerous to go fast in? maybe they're too light?

2] or maybe the more powerful motors just weigh too much... *BUT the 2.0L v4 crossflow weighs 315 lbs, and the 2.5L OMC v6's weigh about 375lbs, which doesn't seem THAT much heavier, does it? the stock 2.5L OMC fishmota's are good up to 175hp i think.

so anyway, why are 16 footers limited in speed? because of being light and dangerous or because they can't take the weight of heavy powerful motors?

just so you know, i'm NOT trying to do better than 55mph with my 16 footer. i'm just trying to learn about theory and tech behind going fast in a boat and curious if size has anything to do with it.


*sorry, i only know OMC's but i'm not OMC mafia. i'd have a merc too in a second, it's just that the boats i've bought so far already had OMC or yamaha installed and running.

-peter

[afr]

wait now there not limitied some sixteens have been in and just above a 100 mph
try this site
http://www.aeromarineresearch.com/index.html

[staylor]

Many of the HP hulls in the 20 ft range are about the same weight- or lighter than your 16 because they use a light lay-up of the fiberglass done mostly by hand with very little "chopped" material which adds weight without much strength. This type of hull usually has a bottom design with a planing pad and often a notched transom, both of which increase the speed potential with a given motor- and which allow the boat to be safely driven at high speeds. When you then consider that these large lightweight hulls are rated for the big V-6s, they can go a lot faster than your heavier 16 with a plain or rounded vee bottom with a smaller motor. There are some very fast 16 ft boats available- in fact, I could top 55 with my old D Class outboard utility, something like 13 ft long, flat bottom, 175 lb hull weight, MK58A Merc 4 cyl with a 1:1 ratio "quicky" lower unit. The MK58A powerhead was rated at 45 hp stock. Weight was 175 hull, 100 or so for the motor, 160 lbs for me and 20 lbs of gas.
Doug

[Sonik]

it seems like a lot of the traditional mono-hull fastboats like allisons and hydrostreams are what i consider to be "bigger" hulls, like 20 feet. [i have a 16 footer, so 20' sounds big to me]. i and a lot of other knowledgeable s and f folks think i ought to be able to get about 55mph out of my 16 footer, [with a 2.0L 135hp v4 crossflow], and i'm fine with that. but i'm wondering why i couldn't or shouldn't go faster with this hull?

I own a 15ft viper that ran 62-ish with a V4 110 OMC. It now has a V6 Merc XR2 150 hanging on it. I'd say your goal is realistic pending 4 things....hull condition (major safety concern), motor health, boat weight, and setup. There are ALOT of variables that play into setup but the most important is what exactly do YOU want to do with the boat. The reason I ask is simply this....if you want to do one thing really well, i.e. top end, then you will most likely sacrifice some other desirable characteristic such as holeshot or an efficient/comfortable cruise with weight in the boat. This doesn't always hold true but for the most part, it is applicable to most situations. I gather that you want a good all-around boat that will still run well and given consideration to all the factors above, you should have it.

i'm going to throw out some guesses here and you guys can comment if you like:

1] is there something about small hulls that makes them dangerous to go fast in? maybe they're too light?

Bottom design plays more into this than weight but is still a contributing factor. (Forgive my lack of knowledge on your hull) Is your hull a pad-V or round bottom design? Pad bottoms, once "on the pad" become a balancing act once you have attained enough speed to run the hull on the narrow surface of the pad and require driver input to maintain said balance. Once on the pad, the is very little boat in the water and as such, water or weather conditions, along with improper driver input can produce disastrous results....i.e. blowover, hooking, swapping ends etc....all of which at speed are bad.

Round bottom boats, like the older glastrons for example, have no pad and are "interesting" boats to run fast in to say the least. Since they have no squared high speed running surface they have a tendancy to wander looking for a "center" if you will. I recently went for a ride in a fellow members CVX18 at over 75mph and it really starts to do some strange things at that speed (if you're used to a pad boat)...more so when water and wind become a major contributing factor.

2] or maybe the more powerful motors just weigh too much... *BUT the 2.0L v4 crossflow weighs 315 lbs, and the 2.5L OMC v6's weigh about 375lbs, which doesn't seem THAT much heavier, does it? the stock 2.5L OMC fishmota's are good up to 175hp i think.

so anyway, why are 16 footers limited in speed? because of being light and dangerous or because they can't take the weight of heavy powerful motors?

Weight distribution does play a big factor in hull balance and overall handling of the boat. This goes back to what is considered safe, as well as what YOU want to do with the boat. For example, Vipers were never designed to run with todays heavier V6 power on them (intended to run inlines) yet, people do it all the time....Ronnie ran his brown Viper to a confirmed 107mph with a healthy V6 Merc back in the day. Keep in mind this was done with a heavily modified, purpose-built boat...and a skilled driver. But doing things along these lines requires sacrifices most pleasure boaters are not willing to make.

just so you know, i'm NOT trying to do better than 55mph with my 16 footer. i'm just trying to learn about theory and tech behind going fast in a boat and curious if size has anything to do with it.

Running surface has alot to do with how a boat handles at speed and different water conditions. Doing 55-60mph in your boat with the 135 is very realistic and easily obtainable I would think.

[pcrussell50]

now _that_ was a hell of an answer, thanks. and staylor too, who has been very helpful in previous threads.

yep, i will be perfectly happy with this hull/motor combo if it does 55mph and i'll leave well enough alone. i'll get a stream or an alli later if i need to go faster than 55.

i does not have a pad, it is a rounded vee on the bottom, but the lowest lifting strakes are quite close together, about the width of a pad, and the way they are angled, it's almost like a pad, visually anyway. i'm sure there is a lot more to a good pad design than merely looking like one.

and staylor, i actually know, [just from online] the guy who built my boat, [sportster mfg. co.]. he's and elderly retiree now, and long-since out of the boat building business, but he says they were premium boats, with no shortcuts taken in construction, and that the boss paid them well, and encouraged them to do the best work possible. i never did ask him about whether it was hand laid or chopper gunned, but i will. thanks for broaching the subject.

-peter

[T-REX]

16' hulls kan be made to run quite well when set up rite....Most good runn'in 16' botes start in tha performance type world...

I have several 16' laser's, vee bottom's, wit slightly modified pads...I have a ski version that now weighs 375#s(hull only), and it had been over 100 quite a few times with Modified 2liters, and 2.4's...My other 16 iz a Laser comp hull, with all wood replaced with composite, and weigh's 265#s(hull only)...

The comp hull I run in DSRA outlaw, 1/8th mile drags...Only rules iz NO nitrous, and min length iz 16'...I started with a 2liter F-1 mota wit carbs, then a 2.4 mod vp carb mota, then went to 2liter F-1 with Madd front and PCU, now have Drag mota with Madd front and PCU...I had a gps in tha bote @ Mount pleasant texas, and run 101.7mph on Saturday, with a 22 wheel, and ran 103.2 on Sunday with a 24" wheel!!...

We work'd on Props before the last race, and knocked off damm neer 1/2 second in 200'(we were juss testing hole shots)...The lift added to the prop to help hole shot made it juss a tad over tha ragged edge, and couldnot make a full pass...

There iz sum lil thangz U kan do to your bottom to make it do what U want it to, but unfortunatlly, tha only way to know iz do it and see what happens...It'z a thrill, but at tha same time, very dangerous...

[RNM018]

It's not that a 16' boat will not run high mph . It's just that it's not as comman to see these smaller boat doing it . Hydro Steam Viper 15' boat in the right hands will get there . Other 16's I've seen make some nice numbers , would be Hydro Stream Ventura , Action Marine 16 , Tahiati 16' with a modified bottom , and a 16' BAJA .

Rich Martin 018

[mach351]

There was an orange 16 Action in Ft Luaderdale that had a 12 inch drag motor on it and went 122 on gps.

[pcrussell50]

Tahiati 16' with a modified bottom ,
Rich Martin 018

near as i can tell, my 16' is a clone of a tahiti, but the bottom has not been modified on mine. still, i'm happy with 55mph out of this hull. i'll get an allison or hydrostream for real speed.

-peter

[4JawChuck]

I am far from an expert in going fast in a small boat, but I joined this forum to do just that in my 16' Tuffy Sportsman. Like you I was not satisfied with the standard answers I heard from most boaters so I began investigating the dynamics and forces at play and also the build quality required to hang a 200HP 2.5L Merc on such a small hull.

Here are some hard facts I have gleaned from the many members of this forum and various websites over the past year while I prepare the hull and come up with a plan.

1) As a boat gets smaller/shorter the ends get easier to swap at high speed, a smaller wave is required to upset dynamics and hull design becomes increasingly important to maintaining control. At some point there is a law of diminishing return where a hull design would only be capable of high speed if the water conditions were perfect (glass smooth), since this ideal is rarely encountered it severely limits the usefulness of the craft.

2) In most cases a vee hull is safest at high speed in shorter hulls, the deadrise is an important factor to being able to utilize the crafts abilities in variable water conditions, not much point in going fishing out on a big lake in a storm in a tunnel hull is there.

3) Smaller craft typically do not have the same hull reinforcement required to hang big horsepower from the transom, laminations are thick and mainly chopper gunned in place with a minimum of stringers. It goes without saying just because it can float with the big motor does not mean it could handle 2 ft waves pounding the hull at 60mph.

4) Wind has a greater effect on shorter hulls at high speed and certainly increases the reaction speed required to catch a "flipover" before it happens, being safe in shorter hulls would require more attention to weather and water conditions and operating far more inside the envelope in case of sudden wind gusts and the odd larger than average wave.

That being said there is nothing stopping a guy from taking the time to engineer a quality reinforcement strategy on the hull and redistribute the weight in the hull to minimize the increased weight on the transom, putting a larger fuel tank farther forward and under the deck to lower the CG are all things that can be done to make the boat safer to drive. Making a boat heavier and more stable can always make it safer...if not slower.

I would suggest that most high speed hulls are larger in length to minimize all these effects in the search of the ideal balance for the least amount of weight in the hull, it could be said a longer hull is lighter than adding 25 gallons of fuel to the hull under the deck to allow higher speeds not to mention more stable in average water conditions.

The other side of the equation is not everyone wants to go 90mph on the water, some of us just want to have a big powerful motor that pops us out of the water with little effort and can cruise at 50mph at half throttle, in those cases underpropping the motor will limit the top speed while really highlighting the acceleration capabilities of the boat. It is likely easier to prevent overrevving the motor by underpropping the motor than to prop for highest top speed and limiting your speed by watching the GPS and the water conditions...both recipes for getting into trouble very quickly if your a little tired or not that attentive.

In my case the prop I have chosen will limit my speed to 63 mph at 5800rpm, easily within the hull limitations and my personal ones. It is likely with the proper prop I could push this engine/hull configuration to speeds up to 80mph+ but it would be dumb to do so in an open cockpit walleye boat. Good engineering practice and common sense still apply of course, as with any modification to a vehicle its best to approach the limits slowly and under controlled conditions with experience and proper safety gear.

One day maybe I can get myself a speed prop and the gods will smile on me and provide a glass smooth lake long enough to wind her out safely and I can post up here a one time GPS videoed run showcasing the capabilities of the boat, but for now I will be satisfied with knowing I can walk softly and am carrying a big stick.

[pcrussell50]

most excellent, chuck. all the best! very enlightening. i'm going to email the oldtimer who built my boat an find out more about the layup.

-peter

[T-REX]

Find out tha material ya bote wuz layed up wit...Tha Kevlar hulls are very thin, and light, but are way stronger than Glass.....

If your happy wit 55mph. U shouldn't have a problem wit dat, no matter what type pad(or lack ov) U have...I had a 16' Carlson with a 115 OMC, it ran 58mpg, and wuz solid az a rock...I put a 150 Mariner on it, and it got damm neer uncontrolable over 60!!!.....Az long az U keep a round bottom bote in tha water, it's a very good ride, but when ya start trimm'in them on tha tail, hold on, it gitz interest'in...

4jaw iz oh so rite about tha transom strength...If your bote iz a hull that wuz intended for HP, then it prolly iz good in tha transom/knee department...But if it wuz juss a ski type layup, it may be like tha baja/checkmate 16's, and leeve a lot to be desired in tha transom strength department!!....Comp Vectors, Lasers, Allisons etc were built for the max HP ov tha day!!!...If it wuz a early 80's hull, tha transom wuz strong enuff to handle max HP on tha market...Juss my unprofessional opinion!!

[scc82]

ive got a stock hull viper with a good 15" 260 on it and it will run over 100 most any day but i prop it to run low 90s and it is a blast. the difference in that boat from 90 to 100 is way more then 10mph, things happen NOW with little time to think. all boats will have a safe maximum hull speed, and after that it takes tons more hp and skill (luck) to fly them. there have been lots of people, me included that have acheived speeds and performance numbers that should not be possible to do, but getting the set up right and the planets alighned properly lets it happen. this is when it gets unsafe. anyways 55-60mph should be no problem and be safe for you as long as your gear is up to par. good luck, be safe let us know how it goes. some pics would be cool too.
stan carson,

[chrispallen]

I have a 16 foot checkmate predictor with a 150 xr2 and i am running 65-66 GPS, for me it was about seat time and finding the balance to set it on the pad and let it go.

http://www.youtube.com/user/parsonsp.../4/P3vEtyFrzsM

http://www.youtube.com/watch?v=tltYIv7XBZU

[pcrussell50]

I have a 16 foot checkmate predictor with a 150 xr2 and i am running 65-66 GPS, for me it was about seat time and finding the balance to set it on the pad and let it go.

http://www.youtube.com/user/parsonsp.../4/P3vEtyFrzsM

http://www.youtube.com/watch?v=tltYIv7XBZU

wow, that's really nose-high in the vids. is that how she runs fastest, or are you showboatin' for the camera? either way, looks sweet.

-peter