Porpoising issue

[overslotter]

I recently got my first boat, a mako 171, and it porpoises real bad. The boat currently doesn't have any trim tabs or a hydrofoil thing. I think it has something to do with the outboard mounting height because it has a 115 ficht and it is only doing 5500rpm wot at 33 mph, do you think that the boat being so small with a t-top has something to do with the low rpm and speed?Even if i have a friend sit infront of the console and load all the gear up front with the engine tilted as far down as it goes, it still has a real bad porpoising problem. Heres some pics if someone can tell me if the engine is either mounted too high or too low, or help me figure out what the problem is:





it currently has some kind of bracket, not really much of a jack plate, but i think its mounted as high as it goes...

[Questsportfishing]

looks to me like you have a 25" motor on a 20" transome .. looks like about 1" low to me so you will have water flooding off the bottom and hitting the lower unit houseing some. the motor should come up some in my opinion and a set of tabs on any mako is a plus and will make the boat feel so much better. a dole-fin or any other model type fin (bass pro sells another type I don't remember the name) will help out on ride and performance. the porp-'in sucks and you will loose so much energy and fwd push because of it.. the lower strake fins on the lower unit I like to see them right in line to 1/2" up from the bottom line so water glides off and then your prop and power is the best. the other thing is that bracket seems to set the engine back more and even 1-2"'s back should mean the equasion just like a bracket the engine starts to move up more. your set up looks to be about 4"'s back ... this also starts to twist your transome way more than the guys who built her wants to see it twisting especially at her age.. they do make other brackets that will save your butt now in the situation you are in...

[jawz12]

looks like you've got a 25" shaft engine on a 20" transom-that's the reason for that aluminum plate,it raises the engine up...
easiest way to tell if the engine is too low,launch the boat,get it on plane and look where the cavitation plates are,see if they're above the water,if they're above,you're ok on height,if they're below,you need to raise the engine...

porpoising is usually caused by too much positive trim,are you trimming the engine too much ???

gimme a little more info here big guy...

[jawz12]

damn ted !!!
you're quick !!! check the time you posted and the time i posted !!!

merry christmas ya stud !!!!

[Questsportfishing]

was that a jack plate in the pic??? It looked like one of those adapter plate thingy's to me... hows the weather up there??? we were in tee shirts and shorts here still... a little windy now though.. he also needs to tell us what year the boat and other stuff also... that boat should ride great on bay to moderate seas after all it's a mako... looks low and also looks like the 2nd hole down in the bolt pic was actually down another hole at one time...maybe a 20" engine package at one time??? ... anyway I have used a jack plate kit on another boat but refused to warrantee or work on it again till it was the right combination of apples to apples (hull to power) kinda thing...

[Questsportfishing]

a bunch so I have more time to think about all you snowed in / iced in creatures not being able to type fast let alone read fast...Hahahahahahaahaha ... merry Christmas...stay warm...!

[overslotter]

thanks for all the help so far...

the hull is a 97 with a 99 ficht, so it was repowered. So you guys are saying that most of my porpoising problem is due to the bracke and rude's shaft being too long?? think thats why im getting such low rpm a t wot too? thanks again for all the help

little big boat:

[Questsportfishing]

the engine bracket does not slide up and down to what I see in the pic.. what is your wide open rpm? are you making a fish tale off each side of the lower unit when you are starting to go fwd? can you take a long straight edge and lay it on your bottom with the motor trimmed down? (lay the straight edge back all the way to the cavitation plates) what wheel are you running also and what rpm...???? it is not too much power for the boat but getting height and prop right with the boats kinda a must to start with..

[overslotter]

wot is about 5500 rpm. what do you mean by "fish tale", is that another name for rooster tale? sorry for my lack of knowledge (first boat) and by wheel do you mean steering wheel? I have one sorta like this without the suicide knob: )

thanks again for all the help

[nautiduck]

By fish tale he means shape of he water around the the bottom of the engine. Wheel means prop what is the diameter and pitch? Figure out how you have your engine trimmed while your running that means how is the motor tilted is the prop level tilted up or tilted down thats a very basic description of trim I hope it makes sense but by trimming the engine you can lift or push down the bow of the boat which will help with your running attitude(bow up or down which can help eliminate poirpoising). I hope this helps answer Quests and Jimmys questions and theyll get you straightened out you have some very knowledgeable people on here and these two really know their stuff