martoiscool Posted January 19, 2012 Share Posted January 19, 2012 Hey raiders, I have been reading Alfa-rosa's post about cavitation and ventilation with much interest and I have a few questions about my own boat. It's a 410 Brooker se-al fisherman with a 30hp mercury bolted to the boat. I have also fitted a SE sports hydrofoil. While I don't have any probs with the above two issues my concern is more with its mounted height and the trim position plus speed. When I bought the hydrofoil the bloke at the shop said it would affect top speed a little. I have noticed this but it does stop the rear from squatting and the nose lifting to the sky and I can plane at slower speeds then before I fitted it. In the following photos hopefully you can see what I mean... I personally think the motor is mounted to low. The first pics are shown with how it came from the shop. With the motor all the way down it locks into place on the pin in the second last hole. I don't think I can raise or lower the motor height without drilling another set of holes (which I'm not keen on doing) to fix this problem. In the next pics I have moved the pin to the third hole and put the motor down. What affect will this have on the way the boat performs/behaves?? How would it affect it if I put it on the very bottom hole?? My last question is I'm thinking of repowering in the next few years as the top speed I get out of the 30 is about what I would like to cruise at but I don't want to be wringing the neck off it all the time. The max hp rating for the boat is 40hp and 110kg. I have done some research and found that there are 50hp motors that come in under 110kg. Would 50 be way to much?? To me the extra 10hp in a 40 might not make much of a difference but I guess it is a third more in power??? Has anyone upgraded from a 30 to a 40 or 50 and. An they let me know how their boat performed?? I thankyou all for your patience and look forward to reading your replys. Sam. Link to comment Share on other sites More sharing options...
Geoff Posted January 19, 2012 Share Posted January 19, 2012 Hey raiders, I personally think the motor is mounted to low. I don't think I can raise or lower the motor height without drilling another set of holes (which I'm not keen on doing) to fix this problem. In the next pics I have moved the pin to the third hole and put the motor down. What affect will this have on the way the boat performs/behaves?? How would it affect it if I put it on the very bottom hole?? My last question is I'm thinking of repowering in the next few years as the top speed I get out of the 30 is about what I would like to cruise at but I don't want to be wringing the neck off it all the time. The max hp rating for the boat is 40hp and 110kg. I have done some research and found that there are 50hp motors that come in under 110kg. Would 50 be way to much?? To me the extra 10hp in a 40 might not make much of a difference but I guess it is a third more in power??? Has anyone upgraded from a 30 to a 40 or 50 and. An they let me know how their boat performed?? I thankyou all for your patience and look forward to reading your replys. Sam. The motor is too low & should be raised so it is at least leval with the bottom of the hull. Having the trim too far in , which appears , from the pic's, to be the case will push the nose down. As a starting point , if you hold a straight edge along the bottom of the boat the cavitation plate should be parallel to the bottom. In respect to the motor size , if the boat is rated at 40hp then that is the maxium you can fit without efecting your insurance or liability if an accident occurs. Weight does not come into the equation. Geoff Link to comment Share on other sites More sharing options...
BWV Posted January 19, 2012 Share Posted January 19, 2012 Yes its too low. I know this isn’t really changing the engine height but it will improve performance. Put the pin in the top hole and post another picture on here with a straight edge from the keel the vent plate. This will cause the bow to lift but that lift will give you better performance. If the vessel feels unstable or chine walks at high speeds with the engine in the top pin drop it down one. You may be able to get away with just moving the pin instead of drilling holes at this stage. With the pin in the 3rd hole in your picture the angle of the vent plate is all wrong, ideally you want that vent plate angled up or parallel with the horizontal plane at minimum not angled down. Geoff is spot on with the insurance and over powered vessels, they will wipe you for just about anything so don't give them an easy reason too. Link to comment Share on other sites More sharing options...
Us13feb05 Posted January 19, 2012 Share Posted January 19, 2012 Hi mate I agree with Geoff the motor is to low Looks like it needs yo go up a inch or so u could use a block of timber on top of the transom to get the right hight shame u have to drill new holes The weight is for 4stroke application as a 40hp 4stroke might be to heavy I think a 3cyl 40hp 2stroke would go well as it would have a bit more torque than a 30 2cyl Cheers clemo Link to comment Share on other sites More sharing options...
martoiscool Posted January 19, 2012 Author Share Posted January 19, 2012 Thanks for all the replies... I thought it was to low..say I was to go to the effort to raise it and drill new holes, would I expect noticeable performance improvements?? As I will be powering up in the motor in the not to distant future I don't want to have two sets of holes plus maybe another set if the new motor doesn't fit the existing holes... I know with the 50hp that it will affect insurance etc but I'm not to worried about that, more curious what speeds, fuel economy etc I can expect with an upgrade. Really appreciate all the replys. Link to comment Share on other sites More sharing options...
BFB Posted January 19, 2012 Share Posted January 19, 2012 manufacturers put a maximum HP rating on their hulls for good reasons. There is no way that I would try to second guess the manufacturer and go beyond the maximum HP as recommended by them. I have seen some horrible problems caused when outboard boats are over powered. Going beyond the maximum HP would not only affect insurances it would affect the legality of the boat. Link to comment Share on other sites More sharing options...
oz_brett Posted January 19, 2012 Share Posted January 19, 2012 Im sure if you searched your area for an aluminium welder he could make a nice job of filling the holes for you for very little $$ I think there usual rates are about $100per hour and the good ones will only charge for 1/2 hour at the most for a job like that. Link to comment Share on other sites More sharing options...
BWV Posted January 19, 2012 Share Posted January 19, 2012 Thanks for all the replies... I thought it was to low..say I was to go to the effort to raise it and drill new holes, would I expect noticeable performance improvements?? As I will be powering up in the motor in the not to distant future I don't want to have two sets of holes plus maybe another set if the new motor doesn't fit the existing holes... I know with the 50hp that it will affect insurance etc but I'm not to worried about that, more curious what speeds, fuel economy etc I can expect with an upgrade. Really appreciate all the replys. Do the simple things first, move the pin, place a timber chock between the outboard and the top of the transom, this may get it a 1 inch higher. Drill new holes as a last resort. Can you slide the engine up and down using the same holes? With the engine up higher and on a higher pin you can expect it to lift the boat higher out of the water and therefore reduce the wetted surface and drag of the hull and reduce the drag of the engine which will result in a faster top speed, better acceleration and better fuel economy. By how much who knows? It might be noticeable it might not be GPS your top speed now and compare. It will be a hell of a lot faster with a 50 and more fun. It’s your call Link to comment Share on other sites More sharing options...
martoiscool Posted January 19, 2012 Author Share Posted January 19, 2012 Do the simple things first, move the pin, place a timber chock between the outboard and the top of the transom, this may get it a 1 inch higher. Drill new holes as a last resort. Can you slide the engine up and down using the same holes? With the engine up higher and on a higher pin you can expect it to lift the boat higher out of the water and therefore reduce the wetted surface and drag of the hull and reduce the drag of the engine which will result in a faster top speed, better acceleration and better fuel economy. By how much who knows? It might be noticeable it might not be GPS your top speed now and compare. It will be a hell of a lot faster with a 50 and more fun. It’s your call the engine is already all the way up on the existing holes so I will have to drill new ones. Is it drilled for a reason or could I just rely on the clamps?? In regards to the 50hp I gues a 40hp would be fine. I mean it is a third more than the 30hp so it should be okay I guess.... Appreciate all the comments and feedback Link to comment Share on other sites More sharing options...
Geoff Posted January 19, 2012 Share Posted January 19, 2012 I know with the 50hp that it will affect insurance etc but I'm not to worried about that. If you have an accident & someone is injured compensation claims can be over $100,000. Is it worth the risk for a few extra knots Geoff Link to comment Share on other sites More sharing options...
BWV Posted January 20, 2012 Share Posted January 20, 2012 (edited) the engine is already all the way up on the existing holes so I will have to drill new ones. Is it drilled for a reason or could I just rely on the clamps?? In regards to the 50hp I gues a 40hp would be fine. I mean it is a third more than the 30hp so it should be okay I guess.... Appreciate all the comments and feedback Just use the clamps to start with until you find the corect height and lash them together so the don't vibrate loose. I have never bolted any outboard to the stern of my tinny's because I just dont want holes in them I just secure the clamps. Edited January 20, 2012 by Whaler 255 Link to comment Share on other sites More sharing options...
martoiscool Posted January 20, 2012 Author Share Posted January 20, 2012 If you have an accident & someone is injured compensation claims can be over $100,000. Is it worth the risk for a few extra knots Geoff good point Geoff!! I certainly don't have a spare 100 000 laying around. Will stick to the 40hp. If I want to go quicker than I should just upgrade the boat.... Link to comment Share on other sites More sharing options...
martoiscool Posted January 20, 2012 Author Share Posted January 20, 2012 Thanks whaler, I'll give the clamps ago and see what difference that makes. Do you reckon that when I do put it at the correct height that I could remove the hydrofoil??? Could the motor being to low contribute to the bow lift and stern squat?? Link to comment Share on other sites More sharing options...
BWV Posted January 20, 2012 Share Posted January 20, 2012 Ideally you want some degree of bow lift when operating at planning speeds, and all vessels squat when operation in displacement mode. You may be able to get ride of the hydrofoil if you like its all really up to you and what you like. As I have said before its one big game of trial and error. You might get it right or where your are happy with or it might take you a few goes. Just have a read of this first http://www.veradoclub.com/smf/index.php?topic=137.0 Link to comment Share on other sites More sharing options...
Juggs Posted January 26, 2012 Share Posted January 26, 2012 It can make a huge difference as you are effectively dragging the cav plate and more leg through the water Just drill new holes and buy shorter bolts and full the old holes use sika flex as well It is illegal to go over plated hp or weights Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now