More Bow lift to help with broaching -Do you lift the motor up a few notches or down?

[Danstu]

Hi

Just wondering if anyone can tell me if lifting the motor a few holes on the transom will help to create more bow lift or will it do the opposite. Coming home from the Barwon banks on the weekend we were running home in a three quarter following sea and the boat was having a tendency to broach a bit which was a bit concerning. It was about a 4ft slop from a north/north easterly which wasn't ideal but it didn't handle these conditions anything like my old 6 meter glass boat did and this is a 7.2 meter plate alloy boat. I was taking it very easy as well as this is a bit scary when it happens. Just feels like the boat needs the bow to sit a bit higher in a following sea but you can only trim it so far before the props lets go. Is this a mater of lifting the motor or a prop pitch issue?? Any input would be great please. Also would lifting the motor reduce prop torque which can make a hull list to port?

Thanks again for any help

[Andy56]

Hi

Just wondering if anyone can tell me if lifting the motor a few holes on the transom will help to create more bow lift or will it do the opposite. Coming home from the Barwon banks on the weekend we were running home in a three quarter following sea and the boat was having a tendency to broach a bit which was a bit concerning. It was about a 4ft slop from a north/north easterly which wasn't ideal but it didn't handle these conditions anything like my old 6 meter glass boat did and this is a 7.2 meter plate alloy boat. I was taking it very easy as well as this is a bit scary when it happens. Just feels like the boat needs the bow to sit a bit higher in a following sea but you can only trim it so far before the props lets go. Is this a mater of lifting the motor or a prop pitch issue?? Any input would be great please. Also would lifting the motor reduce prop torque which can make a hull list to port?

Thanks again for any help

a good place to start is how high above the water whilst cruising is the cavitation plate? How much control over the boats attitude do you have when you play with the trim control? Then i would ask what size motor you have and what your RPM is at WOT. Does the bow rise on take off to get to plane, does it plane?
answering those questions gives us a platform to mull over. All your questions assume these other settings are fine. I bet some of them are not in idea settings, hence your issues.
get the basics right first before worrying if raising ir lowering the motor helps with bow lift. These things tend to take care of themselves with the right settings.

[gazza2006au]

Hey Dan when the following swell picks u up and spears u that is when u need to clean the jocks lol sometimes it can be hairy, here is sydney when its a easterly and im outside rather than rush back and crash and bang over the swell rather sit on the back of the swell and ride it in mate when the swell is rolling in here it has to be doing around 30kph thats an ok cruize speed just as u go over that swell and u pick up speed running down the front it can be dangerous

I also noticed the shape of your hull plays a bit of it the bowed in bow of my old quintrex cruize about made it scary as riding down the front of that swell and being speared isnt a nice feeling where as my mates bowed out bow stacer does it no worries

[Noelm]

You need trim, or weight in the stern, if it's bad, move anything you can to the stern, including people if practical.

[J2DAG83]

Morning mate, my two bobs worth based on experiences with my 6.4 sportfish (aluminium).

Over the first few years of me owning her I had a number of the experiences you have referred to when running with any sort of following sea (there was probably a worse scenario of following sea but can't remember which), I tried all sorts of things in regards to shifting weight (eskies, people), trimming motor etc however had little luck, at a guess I think this probably went on for about 3 years.

After a while I clicked to the fact that my boat has a tendency to naturally lean to the right a little (have checked various things and not sure exactly why) and it only ever broached to the right, couldn't get it to broach left if I tried. Whilst this goes against everything you read (essentially lowering your bow in a following sea) one day coming home wide from rainbow beach I decided to use my trim tabs to remove the lean to the right, I have not had the boat broach since that day.

your boat is likely suffering form an entirely different issue however the above is what I learnt with mine, if it is leaning one way a bit try and straighten the bow to see if it makes a difference?

I find I am still always waiting for it to broach in following seas but can't remember the last time it actually happened

[Dignity]

Dantsu, as AndyAndy says a little more relevant info, also do you have trim tabs, I need them because all my crew are heavyweights and when I changed my layout I forgot to take that into consideration and need the trim tabs to compensate.
Another option is to not run directly back to harbour, consider what the swell is doing closer to land, on the way out you will have noticed there is a slight change in direction, sometimes quite significant. Take a different direction in that is more comfortable, then change direction once you get in close. Usually by the time you get to the Gneerings you'll notice the seas have changed and even closer in the swell direction can be different. A bit longer trip but more comfortable and safer.

[Funchy]

Dantsu, as AndyAndy says a little more relevant info, also do you have trim tabs, I need them because all my crew are heavyweights and when I changed my layout I forgot to take that into consideration and need the trim tabs to compensate.
Another option is to not run directly back to harbour, consider what the swell is doing closer to land, on the way out you will have noticed there is a slight change in direction, sometimes quite significant. Take a different direction in that is more comfortable, then change direction once you get in close. Usually by the time you get to the Gneerings you'll notice the seas have changed and even closer in the swell direction can be different. A bit longer trip but more comfortable and safer.

You calling Craig fat?

[Dignity]

You calling Craig fat?

You and Craig are bigger than I am, that's all I'm saying. 😉
when I put the seat boxes in I should have put the one for the fish an ice on the starboard side as the one there now stores very little weight and I'm much lighter than any of my crew.

[blacklab]

A boat Broaching has to be the worst feeling out on the water. I cant remember the model of the boat, but one I used to out out wide in, with a friend, had a huge tendency to bury it's nose big time, horrible horrible experience.
From memory, he tried everything, fitting a hydrofoil, which made matters worse, trim tabs, shifting weight back, played with motor height, even prop type, but to not really any benefit, his boat just had that trait, that in certain circumstances it buried it's nose. His only remedy was the experience he gathered about when and what conditions it broached.
My understanding, for what it's worth, is you will broach in a following sea, if you get into a situation where the wave pressure/speed becomes faster than boat speed, at any stage, so effectively, he had to expect the worst but drove the boat with all this in mind, he used to have to be on and off the throttle in those conditions all the time and quite aggressively I must add. Effectively, he was driving so as not to broach. It got better going out in the boat with him, he became very aware and drove accordingly. I know he spent a lot of time and money trying to solve his issue.
That comment above about the boat leaning slightly, may well have some value, when talking about a yacht broaching, they all talk about it's lean, if a motor boat broached because of this you would surely notice this as per above.
I've always been blessed with the boats I've owned and currently own, that they were great boats in a following sea and never had any issues, but it's certainly an un nerving experience when it happens, indeed not knowing if it is going to happen.
Maybe your driving habit's need to change as he indeed had too.............

[Andy56]

For sure your driving has to vary with the conditions. My previous boats were pretty well spot on. I could adjust the attitude of the bow at will just with the motor trim. When your following the sea, you gotta stay with it or in front or as i used to do, cut across. If the nose gets buried occasionally, its gotta be a trimming issue. either operator or boat. Operators can be trained and boats need a lot of attention to get right. On and off the gas is a prop issue. Going 4 blade helps to maintain momentum where as a 3 blade can want to run off. Thats not to say its a wrong prop, just different props have different effects on performance. 3 blade is great for water sports and 4 blade is better for adverse conditions. Most of us just couldnt be fagged changing prop every second day. So its a compromise.

[Noelm]

Broaching is not just having the bow go under, it's when the boat spears off to one side, and some boats do it when not trimmed right, some just do it, regardless of what you do, most can be driven to almost eliminate broaching, but, if your boat is just made that way, then hang on is the only option.

[Andy56]

i bow to your greater experience here Noelm. I havent had a bad boat yet, touch wood. But if you just think of the dynamics at play, its amazing most boats dont have a mind of their own, lol.

[Noelm]

I haven't had a boat that couldn't be driven right, but, my mate had one that was "bad" it was a common brand, and it didn't matter what you did, it would just sheer off to either side at near right angles, only happened if the sea was directly behind you, side on, head on quartering it was fine, but, directly behind, it was exciting to say the least, we fish a FAD that is NE from our ramp, coming back in a summer NE wind was a lucky dip.

[Andy56]

NOELM , that hull / model still around?

[Noelm]

An old Easyrider, plenty of them built, lots the same as my mates, and they were fine, but his was shit, he put up with it for about 5-6 years, then sold the boat.